Yes, as desi said, compatibility is a little wishy-washy, mainly when it comes to imported games from America and Japan. All PAL games work fine.
As with jac33au's problem, I haven't had that problem myself. There are people out there who have had similar problems, but it's not anything to be worried about.
There is a new firmware update for the chip coming out soon, which will hopefully increase compatibility for more NTSC Wii games on PAL consoles.
26/07/2007
Mario and Sonic at the Olympic Games
Gold Coast, Queensland, Australia