I downloaded ubuntu-11.04-desktop-amd64.iso and used Universal-USB-Installer-1.8.6.3.exe to format my USB stick und put the ISO on it. When I tried to install from it, I've got a kernel panic just like here, except for the version number (mine was 2.6.38-8-generic #42-ubuntu). My ISO image seems to work, as I installed it into a VMWare player without problems. Booting Linux from USB works surely too, as I did it some time ago with an older Ubuntu version.

I can imagine things to try out, e.g., write the image again, try another version, pray, look for patches, etc. However, I'm looking for a time-efficient solution, something what most probably works. An advice of the sort "wait two weeks until it's surely fixed, then download again" is acceptable, I'm determined to switch to Linux, but it can wait a bit.