Plus 1366 supports triple-channel RAM, 1156 is only dual channel. Doesn't make a difference to most people but it's a difference nonetheless.
At the end of the day, 1366/X58 is going to be the high-end platform with 1156/P55 the mainstream. Unfortunately making the choice now means you have to stick with it.
Both have a future, but the nice/stupid processors like the hex-core i9 Gulftown will be on 1366. If you're not a high-end user or serious gamer then I'd save some cash and go 1156 because you won't use the high-end features (although SLI and Crossfire will be on 1156).