Like the current generation LGA1156 and LGA1366 platforms, the Sandy Bridge CPUs will be separated into two different markets. One will be consumer oriented, and one will be for enthusiasts (read: early adopters who can afford $1000 CPUs). All the CPUs will be based on a 32nm manufacturing process, with some enhancements unique to the next gen chips. They are expected to utilize Advanced Vector Extensions to greatly improve throughput of parallel computing tasks. Intel is also looking at implementing Advanced Encryption Standard Acceleration which would provide better performance in encrypting and decrypting data.
The consumer version of Sandy Bridge will take the place of the current Clarkdale and Lynnfield CPUs (the Core i3 and Core i5). However, these chips will use LGA1155 instead of Nehalem's 1156. Yes, there will be just one fewer pin, and by all accounts the sockets will not be compatible. To really drive the point home, Intel has also moved the position of the notch to ensure the chips will not physically fit. But it's not all bad news.
The replacement for 1366 is expected to be the LGA2011, which is sort of odd as it's debuting in mid-2011. These chips will be the Sandy Bridge E ('E' for enthusiast apparently). You can still expect Hyper Threading and Turbo Boost technology. This socket is going to be much larger than the current 1366 in order to accommodate quad channel DDR3 RAM. You can bet the larger socket means these chips won't work on older boards. Also, you might need new RAM if you want the quad-channel support. There's also going to be support for PCI Express 3.0 at long last bringing 32 lanes of bandwidth. The platform will be able to split those lanes into either 2x16 or 4x8 configurations depending on the number of GPUs.
Intel has been dragging its feet a bit on implementing new technologies like SATA 6Gb/s and USB 3.0. This has led some manufacturers to put additional controller chips on their motherboards, or offer add-on cards, that add the functionality. Both the Sandy Bridge platforms will support the new SATA standard, but there will NOT be USB 3.0 support. This leaves us a little confused and depressed.
The LGA 1156 didn't come out until even later than the LGA1366, as it was paired with the Lynnfield launch in September 2009. Consumers that purchased an LGA1156 motherboard can expect to have their setup obsoleted by the first quarter of 2011, or maybe even late 2010. So they are actively supported for maybe a year? It's interesting that Intel is moving ahead with a new architecture so soon. Before Nehalem, the reliable LGA 775 socket lasted all the way from Pentium 4 through Core 2 Quad.
The upshot is that starting next year, no matter what board you have, Intel's new CPUs will not be available to you as drop-in upgrades. There's no way to know what the performance of Sandy Bridge will be like, but will it be good enough to get this bitter taste out of our mouths?