Well, as far as we know Intel is committed to the socket for the foreseeable future, there are multiple CPUs available from launch with a few more planned, but don't expect the wealth of choice currently available for LGA775. We don't know how well Lynnfield will perform in comparison to both LGA775 and LGA1366, but while the PCI-Express-CPU-Memory transfer will be more efficient there will be less memory bandwidth to play with. How important either of these factors are in Nehalem - compared to Penryn - will provide a key to the answer of how important the Lynnfield launch will be and whether it will be worth waiting a long time until Q309 for an overhaul upgrade.
Both LGA1366 and Socket 940 used expensive, niche memory that's specific to its platform, but the advantage Intel's new setup has is that it will work with most DDR3 already available - so if you already own a dual channel kit that will see you through for the time being. AMD's socket 940 on the other hand would only work with ECC DDR memory and there was no performance market for this.