I'm getting this also. Hangs for about 4 seconds after clicking maximize. Kubuntu 11.04 64-bit (and all updates as of May 10) + nvidia 270.41.06. I use konsoles and emacs all day for work. There are a few other reports on the web, but none with replies confirming an issue.
Wait, turning off desktop effects and rebooting seems to have cured it. Also system settings -> hardware -> power management -> power profile -> disabled desktop effect -> on profile load.
Oh, I see this is a fairly common issue, reading the Arch linux board.
> Comment by James Jones (jajones) - Thursday, 21 April 2011, 16:53 GMT-4
> NVIDIA is aware of this problem, and we have reproduced it internally.
Multiple threads claim the x.org event queue (EQ) is being overflowed by the gfx driver.