Thisius, you are thinking ahead to solve problems you don't even have to deal with yet. That's a hallmark of good leadership. Now is a great time to start planning how you'd like to handle the first few weeks of Cataclysm. Here are a few tips and considerations.
1. Have a plan. I can't stress this enough: Don't just let things play out. Keep everyone focused on the goals of your guild, whether that's putting together a functional raid team, amassing enough 85s to run rated battlegrounds, or some other mission.
Before the expansion hits, communicate those goals to your guild along with how you plan to achieve them. Your members will feel a lot better about sticking around if the guild leadership has a plan and is already focused on approaching the endgame.
For PvE, your plan should include the loot system you'll be using, the level of raiding you'll be focused on (10 or 25), and whether you intend to use lockouts to progress or reset them each week to farm the bosses you've already learned. Concerns that will crop up farther down the road can also be addressed now: alt runs, heroic modes, legendaries, achievements, and so on.
2. Organize group activities during the leveling process. One way to maintain guild cohesion and camaraderie is to schedule official nights for group-oriented leveling activities. Set aside at least two nights per week specifically for group quests, dungeons or PvP. Certainly your guild members will do these things on their own, too, but for members who hate to PUG anything or who have limited playing time, it will be helpful to know that they can group up with others in the guild on specific nights.
3. Don't rush anyone. No one likes to be harassed to level faster. Inevitably, some players will go hog-wild, devouring all of Cataclysm's content as if it were an eating contest (and Blizzard apparently wants people to view it that way). Other players will savor each morsel at their own pace. Leveling for the first time in an expansion only happens once for everybody. Don't ruin it. However, you can provide motivation to level quickly.
4. Set a date for the endgame. It doesn't matter if the date is optimistic; just schedule something at max level. Put a raid or other event on the calendar so your members have an idea about when you'd like to get started. It will give them a goal to shoot for and provide a sense of purpose to leveling. Officers shouldn't have to resort to irritating prods.
For a typical guild, I'd give your members 10 to 14 days at least before you schedule the first official endgame activity. You could also poll your members to find out who is planning to level as fast as possible and who is going to take their time. Then adjust your date forward or backward based on that information.
Make it clear that the officers will do their best to make sure that the scheduled event occurs even if they have to find players from outside the guild in order to field a full group. You don't want to give people a reason to level quickly that ultimately evaporates. They'll feel cheated.
Based on statements from Blizzard, guilds may not find success in raids right after hitting 85 without any prep work (like we did at 80 in Naxxramas). However, I encourage you to at least try with whatever you have at the time. Unlike the dungeon finder, raid portals can't tell you you're undergeared. Even if you fail, you'll still learn a lot about that first boss that will help you when you come back with a better-geared group.
Ultimately, you shouldn't need to provide artificial incentives for players to reach the cap. Being the first to experience the endgame is reward enough. On the other side of the coin, don't punish members who haven't made it to 85 yet. Missing the first raids or rated battlegrounds is punishment enough.
That's all for this week. Visit the Officers' Quarters next Monday for more leveling tips!
Send Scott your guild-related questions, conundrums, ideas and suggestions at firstname.lastname@example.org. You may find your question the subject of next week's Officers' Quarters!