I dug deep into the app using GDB but the results were disappointing. I don't think there is a way to do this currently. Here's what I learned:
First you can change the speed of switching into Mission Control (still called Expose in the prefs). To do that just enter this command:
defaults write com.apple.dock expose-animation-duration -int 0; killall Dock
And to go back to defaults run this command:
defaults delete com.apple.dock expose-animation-duration; killall Dock
Secondly there's a reference in the binary to
fps-spaceswitch (frames per second spaceswitch). I messed with this for a while and also tried variations on this such as
spaceswitch-animation-duration without luck.
Unfortunately (at least as of 10.7.1) there does not appear to be a way to change any settings related to this animation.
I filled a bug for this with Apple. The Radar number is 10073864. I would encourage you to also file the report at https://bugreport.apple.com/. Note in your description that it is a duplicate of the above bug report number to help the support staff categorize and prioritize this bug.