In Mission Control, pressing Command+M enables motion blur for all Exposé animations within Mission Control and Exposé in general.
It's a fun effect, but probably a little heavy for older Macs. Besides please be warned that the effect is obviously disabled for a reason: it's really buggy, and will likely crash your user account by logging out without any warning. Thankfully it's OSX Lion, so logging back in will recover everything.
Disable the effect by pressing Command+M in Mission Control again, or by logging out or rebooting your Mac.
[crarko adds: It's there, minimally, on my old MacBook. A couple of people submitted this hint (one anonymously) and I've combined them a bit here. It was a split decision between them that this may also apply to Launchpad; I didn't notice anything when I tried it there.]

