Is it worth it if I only use my computer for web surfing, word, excel documents and the occasional dvd movie? I just got my 2.2 macbook last week.
Not much, really. The biggest upgrade in terms of bang-per-buck (or quid) is the "free" boost to 2GB of RAM and the 250GB hard drive. If you're going to upgrade to 4GB anyway, then that bump is moot.
Someone over on the MBP forum posted a Geekbench processor benchmark for the 2.4GHz Penryn MacBook Pro (same processor/FSB speed as the 2.4GHz MacBook). The score was 3083 I believe. My 2.2GHz MacBook scored 2880 (just ran it). Not a big difference there (158 points). To put that in perspective:
2.0GHz MacBook Core Duo = 2411
2.0GHz MacBook non-SR Core 2 Duo = 2534
2.0GHz MacBook SR Core 2 Duo = 2659
2.2GHz MacBook SR Core 2 Duo = 2880
2.4GHz MacBook Pro (Penryn) C2D = 3038
My machine is 16 days old, so I could also (at least try to) exchange it, but I'm not really going to bother. I've already upgraded it to 4GB of RAM, I still haven't filled the HD (I don't keep tons of movies/music/iPhotos on my laptop since I also have a desktop as a main machine), and I essentially only do text & minor graphics on my laptop (Mail, word processing, Keynote/PowerPoint, web, OmniGraffle, Preview for PDFs and minor jpeg editing with Pixelmator or Preview).