Although the lack of a jungler is generally the hallmark of low-skill play, the extra teammate can be a great asset. If you're looking to control a particular lane, putting an extra champion in that lane will almost always ensure dominance. It is the rare player who can handle two champions by himself without getting behind, so bullying in this way is always at least somewhat effective.
However, fielding no jungler means that you are surrendering control of your jungle to the enemy. If you're intending to run without a jungler, you should focus heavily on warding your jungle entrances and ganking the enemy jungler as he enters your territory. If you do not control the enemy jungler, he will get very far ahead and be able to feed his own jungle buffs to his team while using your jungle buffs to clear spawns and gank. All of your lanes need to pitch in more for wards in this situation, and in my experience, the extra warding almost never happens.
If your team happens to be in this situation, the person in the 1v2 lane should be instructed to play ultra-defensively, hug the turret, and do her best to stay in experience range without putting herself at risk. Your team's jungler should not put too much emphasis on trying to "save" the lane; it's better to build advantage elsewhere instead of trying to break even on a losing lane. The jungler should ruthlessly steal enemy buffs and control the easy jungle camps (especially the enemy wraith camp) in order to limit the enemy's extra jungle gold.
Almost every time I have been put in this situation, my team has won handily by either having a decent player in the 1v2 lane (< 2 deaths in lane) or absolutely crushing the enemy with our jungle advantage. I cannot recall a game in which my team lost with a jungler when the enemy had none, though I have a few victories where my team did not have a jungler but the enemy team did. The difference was really just warding jungle entrances to prevent counter-jungling. Still, a team with a jungler wins more often than not, simply due to the advantage of an unpredictable ganker and the bonus jungle resources.
Alternate duo lanes
It is fairly unusual to see the duo lane be somewhere other than bottom lane. The reason for a duo bottom is mostly the presence of the dragon and the overall difficulty in ganking mid lane. It's easier to gank a side lane than it is to gank mid, so the bottom lane is a duo lane (insulated so an advantage situation is 2v3 instead of 1v2) and the top lane is a tanky bruiser lane.
Putting the enemy in a 1v2 situation is always difficult, and the intitial shock of a duo lane can result in free damage or a kill before the enemy really understands how to deal with your lane power play. However, as skill level rises, enemies in an advantage lane will tend more toward ultra-defensive play and will avoid giving away too much. Even then, you still might have the advantage, since your team knows you are moving the duo lane elsewhere but the other team does not until it sees the doubleteam in action.
This strategy trades one advantage lane for another, so you are relying on the isolated lane to not feed (very hard in a solo bottom unless it is not a carry down there) and on exploiting your numbers advantage to get kills and shut down the enemy in your advantage lane.
A lane swap can be an effective counter to this tactic. If the enemy is running a duo mid or duo top, you can swap the carry/support to the duo lane and play normally. If your outnumbered ally feels comfortable with fighting at a disadvantage, this puts you at a substantial advantage overall if your duo lane can exploit your own numbers advantage.
Remember that each team has five people and that for every numbers advantage you try to eke out somewhere, you are losing that advantage somewhere else.
The roaming support was an old metagame staple before it was phased out. It still sees some use in mid-level play and by "seasoned" low-level veterans. The main problem with the roaming support is that the support tended to get very far behind; despite the game's having a much faster-respawning jungle than in the old days, there are not enough jungle spawns for two people to roam and get respectable experience and gold. This puts a lot of pressure on a roaming support to make some magic happen in lanes, which can be tough.
Despite the name, the roaming support is almost always some kind of powerful ganker who is less reliant on gear. A decent example is Nautilus; Blitzcrank is common in the role, too, but any ganking jungler (such as Sejuani or Hecarim) performs fairly well at the job.
The biggest strength of a roaming support instead of a laning support is the unpredictability that comes from a roaming team member. This makes it more powerful in generating kills than an alternate duo lane. A roaming support is essentially a second jungler who can be used to help invade the enemy jungle as well as gank. This makes it a very strong potential strategy.
The main strategy for defeating a roaming support is to ward. Your team's jungler should ward heavily, and all lanes should purchase extra wards. Use them to deny easy access to your lanes. If you have the enemy team's jungle exits warded, that will make it very hard for the enemy to move around and score ganks.
Rather than change the numbers in lane around, a team may decide to simply run an unorthodox composition. I've seen Katarina/Irelia bottom lanes, and I'm well aware that Leona/Jarvan is a fairly well-accepted alternative to a traditional carry lane. Others may simply choose to lane a bruiser or carry in mid lane and put other champions elsewhere.
The best reason to use an alternative lane is a bad matchup. If the enemy team has a Kassadin, for instance, laning a traditional mage in mid lane is very hard. The best choice for your team is to put your top lane bruiser in mid lane and move your mage to top lane to avoid Kassadin. If the enemy team switches lanes, you probably should too. There's no point in trying to face off in a Jax vs. Teemo battle when the little mouse will fill your veins full of toxic venom. Swapping with someone else lets you avoid the embarrassment of getting beaten by a hamster.
My personal rule of thumb is that if the enemy team runs any support in the bottom lane other than Soraka, I always play very cautiously until I know how the enemy support wants to play. Silly lanes like Garen/Katarina can be handled pretty easily underneath my turret, especially if they try too hard to push the lane. This goes double for replacing the carry; if the enemy team fields someone like Garen instead of a normal carry, I almost always err on the side of caution. Garen can easily cut off 70-80% of a carry's lifebar, so keeping him from using Decisive Strike to cut through my life is a definite priority.
Of course, I prefer standard play because "playing normally" puts a greater emphasis on skill. If I fight while playing standard and lose my lane, it's because I (or my partner) got outplayed. If I play a goofy gimmick and lose, it's still my fault, but it might be just because the enemy was ready to counter that kind of strategy and not because he was better than I was.
We understand what it's like to climb the skill ladder in League of Legends. The Summoner's Guidebook teaches you the tools you need to get a competitive edge. Whether you're climbing the ranked ladder, playing Draft Dominion, or getting crushed by intermediate bots, every enemy has a weakness. And every Thursday, Patrick Mackey shows how you can improve improve on yours.