We've had this conversation so many times now my head is spinning lol.
Whilst the Sandybridge chips indeed look very fast and cheap they are limited to running dual channel. This means that 1155 is an extension of socket 1156.
The replacement for 1366 is nearly a year away, so if you were expecting cutting edge performance from Sandybridge then I am afraid you were wrong. Sure, they'll no doubt be fast chips but they're mid range chips.
For example. An 1156 I7 (870 or what not) can not even sniff the arse of a 950 say. And, the 870 chip costs more than the 950. This is due to the 1366 board costing more money because it's far more technologically advanced.
1366 boards however can be had for a song at the moment. Pfft, try that with an 1155 board. IMO buying anything at release means you have more money than sense but hey, I guess I've just not been in a position to throw money away for over a decade and nor would I want to.
The bottom line is if you want a new computer and don't cry every time something newer and better comes along to replace it then by all means buy a 1366 based system. Because if you buy an 1155 based system it won't be long before you feel exactly the same way. It will be replaced, it's not a matter of if but when. And when it does no doubt you will kick yourself if you're the sort of person that's into kicking himself/herself.
Also, expect teething issues with drivers, poor boards and all of the other things that tend to surround new hardware. Meaning you can expect to wait on a new bios.