The Inquirer reports the LGA1366 socket for Bloomfield and Gainestown processors will be about 20% bigger on each side and also a lot more robust. The socket will feature a metal backplate and there will also be an improved retention mechanism.
Take a look at this LGA1366 test board for the Bloomfield. While the front CPU socket insertion seems the same as right now, the back portion has a proper metal back plate which, via four screw holes, holds the CPU socket firmly without banding under, say, heavy fans.
But, hold on, at a second glance, even the front isn't really the same - there's an independent loading mechanism - ILM - instead of the direct socket loading used right now. Take a look at the mounting process from these slides.