We watched The Hitchhiker's Guide to the Galaxy last night. You can read M's review of it here.
I was a huge HHGttG fan back in my youth; I listened to the original radio drama, had the later BBC audio version, watched the television series, read the books, own the scriptbook for the radio series and dressed up as a galactic hitchhiker for Halloween in sixth grade. That said, I wasn't dreading this adaptation (heck, Starship Troopers is my favorite book and I enjoyed the non-adaptation movie that bears its name).
Before seeing the movie, I was wondering how casting Mos Def as Ford Prefect would work out, but I think he did a solid job.
Overall, I enjoyed the movie. In some points it felt a little slow, and there was a minor involuntary protest when they added things, but really, there's no canonical version of the HHGttG, so no worries. The original radio drama has some things I loved that Adams chose not to put in the books (the shoe event horizon, Lintilla and the Allintils) and the books added many things that weren't in the radio drama. A quick run through the trivia at IMDB tells me that all new ideas in the movie were added by Adams, with other writers just there to make sure the screenplay was coherent. So, indeed, this is another in the line of HHGttG versions.
My main complaint matches littlestar's -- movie Arthur was just too spineless. Arthur in the books and radio show is clueless and generally overwhelmed, but not quite as cowardly as portrayed in the movie. The feeling I like for Arthur is not that he's afraid, just that he's overwhelmed.
A fun rental, and I do like how they handled the Guide itself.
...and I just added this to my Amazon wishlist.