Technically, the Guide turned 31 earlier this year, since the first broadcast of the radio series (the truest version of the series, IMHO) was on March 8, 1978...

"The wildly imaginative and funny science-fiction novel spawned four more books, a radio series..."

Yes, I believe it was a copy of the HHGTTG novel that had the good fortune to fall through a wormhole in space spawned the radio series that preceded it by several years.

I agree that the movie isn't the best incarnation of the series, but Douglas Adams did actually have a hand in the development before his death. He was always into the story changing a bit more in each version of it, from radio to play to miniseries to movie. He didn't want them to be the same. I do think the movie would have been even better if he hadn't passed away and had been able to keep a close eye on it.