Seriously though, there is little for fans to worry about. If it's rubbish then we can forget it, and if it's good then we'll be shouting from the rooftops. Don't see the point in being grumpy about it, it'll work or it won't.
Well personally I don't think it is as quite straight forward as that. There probably is only going to be one film made of this classic so if they balls it up there is going to be little hope for another better version. Just think how excited we all were when we heard the film was going to be made. Expectations are very high, as they were with Lord of the Rings. Imagine how disappointing it would have been if LOTR was anything but the epic it was...
I think the main thing to hope is that they keep as much as the original radio script as possible bacause as Ian has already pointed out - so many people do know masses of it word for word. It's a little like Monty Python in that respect.
It's a big shame that Douglas Adams isn't still about to keep control on things. Actually it's a big shame that Douglas Adams isn't about period.
On the flip side though, so far there has been the Radio Show (the best adaptation IMHO), the book, the TV show (good grief) and I even saw it performed as a play.
Now - the TV show I think we can all agree was pretty blake7esque (or Naff for those that don't know what Blake-7 was), but having said that the words were so good that it was still eminently watchable by most HHGTTG fans. It's the words that are magic. That's why the radio show and book were so good as we could create our own mental imagery.
Personally, I think the film will be great whatever it's like - as long as the words are still there.