I know this has been discussed/mentioned/asked here before, but I don't remember if anything useful was ever concluded, and I can't seem to find any answer when searching neither the board nor Google.

The question is: Sometimes OllyDbg itself seems to take 100% CPU when the debugged process is running. Why is this, and can it be/has it been fixed somehow?

You will find references to this problem e.g. here:

http://www.woodmann.com/forum/showthread.php?t=8533

and here:

http://www.woodmann.com/forum/showthread.php?t=9846