"Westmere" covers a pretty broad spectrum. The server and enthusiast chips (essentially Core i7 shrink) are Socket 1366. The desktop/mainstream chips are Socket 1156. Mobile is something else entirely.
We all wondered that initially, but from what I've read, Intel has pretty much confirmed the 6-core Westmere desktop CPU will be a drop-in replacement for the i7 Bloomfields. Most likely you'll have to get a BIOS update to get it to work however, so keep that in mind when choosing an X58 mobo brand.