A friend of mine asked me to have a look at her computer, because it would not boot up anymore. It just showed a splash screen of the BIOS and waited there for several minutes. After that time it would suddenly continue booting, with normal speed and without any further problems.
I had seen such a thing before, however not that early after switching the power on: In one case an iPod had been connected to a USB port, another machine had a USB card reader attached. In both cases the machine hung right after all the power on self test (POST) messages and hardware detection at the point where it normally boots from a configured boot device. On both computers disconnecting the USB devices solved the delay immediately. It does not seem to affect USB devices other than storage devices. A mouse or keyboard did not cause any problems.
The computer at hand now had an internal card reader. I opened the case and unplugged it from the mainboard. That made it run through the POST in no time, no hangs, no delays. I could even plug it back onto the board, without getting the problem back (I wonder what caused it to fail in the first place, the reader has been there ever since). Seems to be some sort of a common BIOS or maybe even a hardware problem (just Google for "usb boot hang bios"), but it sure as hell is very annoying, especially with internally connected devices that cannot simply be unplugged.