I just bought the ultimate Hitchhikers Guide, and I'm almost done with the first book (I'm not a reader at all). I have to say that I've been missing out all this time it's been out :P the book is hilarious. What do you guys think of it? And is the movie worth a rent?

Be glad you read the book first. While the recent movie is not necessarily bad (I liked it), it does take some liberties with the book that some find unforgivable. From what I understand, the original BBC radio series and the later TV series are infinitely better than the movie was.
The books are fabulous... life-changing even. I never leave my house without a towel anymore and the words "Don't Panic" are my personal mantra. Anecdotes from the book pepper conversations similar to the way Monty Python skits seem to pop up in everyday life. Douglas Adams was one of the greatest absurdly comedic minds of our time.
Did I mention I liked the books?

The books are absolutely wonderful, and I agree that they can be life changing.
When I left for my current travels I set my Facebook status to ...is a hoopy frood, and all my friends got the joke. :)
The books are classic British absurd comedy, similar to the goon show and Monty Python.
I haven't seen the recent movie, but the old BBC radio production and TV show are very good (the horrible mid 80s special effects in the TV show fit the feel of the show very well, so don't detract at all), and are well worth listening to/watching.

I recently saw the bbc radio show and was not sure if it was worth it. Ill definitely pick it up now. I have a 1 hr trip to my university and then back to town. So it would be a nice distraction.

I for one think the movie completely failed to capture the feel of the books. I would agree that the books are life-changing, in a hard-to-describe way. I just know that without having read the Hitch Hiker series, I would be a different person than I am today. And almost certainly a much more boring person ;-)
My favourite HHGTTG moment was the very first time I read the first of the books. The beginning of chapter 7 hit me so hard, it is the only time in my life I can recall being on the verge of actually throwing up from laughing so much :-D

"Ford, your turning into a penguin. Stop it. "

I agree that the books are exceptionally good. At least, if you like the style. They are hilarious :-).
Also, not only are they worth a read by themselves, once you read them, you'll get sooo many references and easter eggs in so many games.
Ah, quoting time? ;-) Then...
"A million-gallon vat of custard opened itself opened itself over them without warning.
-But what does it mean?- Cried Arthur.
-What, the custard?"
:-D

"Warp travel gives you the horrible feeling of being drunk."
"Whats wrong with being drunk?
"Ask a glass of water."

(Ford, referring to Hotblack Desiato)
-He's spending a year dead for tax reasons.

I have pity in my heart every time I read about poor Mr. Prosser...

Ah, yes, that one horribly fails in Swedish as it specifically takes the meaning of "someone/thing is drinking me", not the ambivalence of the added "or I have been drinking too much".

"Nothing travels faster than the speed of light, with the possible exception of bad news, which follows its own special laws."

I picked up Hitchhiker's Guide quite randomly when I was 12 while looking for something to do a book report over, and that's the book that got me into reading.
Wowza, I never really thought about it before, but if not for that incident, and even though I don't even like Douglas Adams so much anymore, I wouldn't be an English major reading and writing all the time while being a pretentious tit. I'd be a completely different sort of person. Huh.
Advice: Stay away from the film (it did OK in transferring some bits of the Guide itself to the screen, if i remember right--and the dolphins at the beginning), and hell, I'd even advise staying the hell away from the original BBC TV series. I thought it was just as bad as the movie.
For Douglas Adams, his two Dirk Gently books are pretty enjoyable, and I really recommend his Last Chance to See, which may sound boring, but it's great. Easily my fav. book from him. The last two books in the Hitchhiker series are kinda garbage, so don't expect a lot.

The movie is not as bad as people make it out to be and it has a few good moments. The books, radio and TV shows are a different league though.
Also a fun fact is Douglas Adams was once a scriptwriter for Doctor Who back in the Tom Baker years so there are several cheeky references by Adams to his own creation. The Doctor reading Oolong Caloophid's More of God's Greatest Mistakes for example.
More recently the Tenth Doctor remarked when he noticed he was in a dressing gown that it was very Arthur Dent.
Oh and the Infinite Improbability Drive is a component of Star Trek's Warp Drive. In Star Trek TNG it was on one of the status monitors in engineering.

"Time is an illusion, lunchtime doubly so."
The three books of the trilogy proper were quite good. After that I became more and more disappointed. Douglas Adams seemed more depressed each book. I did enjoy both Dirk Gently books though