Yes, I finally got around to catching The Hitchhikers Guide to the Galaxy last night, and I can honestly say that it could have been much, much worse. Douglas Adams has a style and humor not easily replicated, much less transferred to a different medium. That said, the feature film does a good job of conveying said style, or good enough that those not versed in Douglas Adams can still have a laugh or two.
Overall, I'd say about 50% of the material is sourced from the original book, while the remaining percentage is thrown in as screenplay adaptation, i.e. the Arthur/Zephod/Trillian love triangle. If you're one of those people that cursed the Lord of the Rings movies for being unfaithful to the books, then you won't like this, either.
So that said, I still eagerly await Forza Motorsport like a little boy waiting for chocolate chip cookies to come out of the oven. But, like the responsible pessimist that I am, I still hold some reservations. I still fear the inevitable 13 year-old AOLers and rice like a European fears the Plague, and I know there are gonna be Xbox sackriders abound, trying to tell me that Forza > GT4. I'll play the finished product a good bit before I decide if it's worth arguing with them.