While the swords play-style tends to revolve around Cheap Shot and Sinister Strike, dagger rogues lean more towards Ambush and Backstab. Why? Well, Sinister Strike is best with a high-average-damage (read: slow) weapon, and daggers are generally fast. And honestly, Backstab is a lot harder and more time-consuming to pull off in solo PvE than Sinister Strike. Sure, you can gouge and run through the mob, but it's so much easier to just stand there and whack it in the face with something big and sharp.
Between sword and mace spec, the 5% white damage increase (actually a bit greater, since it can proc off special attacks) from sword spec is believed to outweigh the incoming damage decrease offered by mace spec, and the +5 weapon skill for maces is just not that handy when not fighting mobs 3 levels above you. Higher level mobs are the rule in raids, but not elsewhere. Therefore, the edge in solo PvE goes to Sword Spec.
In group PvE, on the other hand, it's dead easy to get behind the mobs, since they're generally held in place for you by the tan. In fact, you should get behind the mob even if you're just going to use Sinister Strike, since when you do it from behind, they can't block or parry (though they can still dodge, and you can still miss). Since Backstab is easy to pull off in groups, and it does do more damage than Sinister Strike, dagger rogues tend to top the charts in raids and take the lead in group PvE.
That leaves one playstyle, PvP, and one weapon spec, Maces. Conveniently, it seems that mace spec is (slightly) the best-suited weapon spec for PvP, simply because stuns are very useful against other players, as a means of control. The same arguments as in solo PvE apply to drop dagger spec from the running, and the 5% more white dps that sword spec gives is just not as useful in PvP as a few random stuns are.
So, as a certain legendary thread might have put it, does mace rogue = PvP server? I hear mace rogues will smash faces in PvP...