Although there is an official mobile version of IMDB it doesn't seem to be working and hasn't been working since I first tried it a couple of weeks ago.
There is, however, an alternative: Mdog's interface to IMDB
It's very functional and is perfect if you want to check some basic facts while watching TV or a DVD (more likely a DVD in my case). Admittedly some of the functions of the "normal" site don't work, but I can live without them. In any case it's better than having to boot up my laptop just to check some movie trivia 🙂
UPDATE August 2011
Checking my stats this post is obviously still quite popular 🙂
IMDB have now got a mobile version of the site and also have apps for popular handheld devices such as the iPhone and iPad.