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).
If your into gaming and want to CF or SLI go with the I7 on the 1366 platform. Micro center has the I7's 920 for $199 and can not be beat on price. Given the x16x16 PCI-E lanes, much better choice then I5's.