I tend to agree with Bob. I've never had AppleCare on a desktop and never regretted not having it. I've only had one issue within the first year - the defective G5 with thermal overruns, which went back to the Apple Store for exchange within 36 hours! Any other issues have been after AppleCare would have expired. And then only one problem - power supply on my G5 died at the 3.5 year mark, and was a $425 repair. On our laptops, I've bought AppleCare 2 or 3 times, but never actually used it either. (Again - on 4 Powerbooks/MacBook Pros, only one issue and that was a keyboard gone wonky and it went back after 3 days) On my last one, I didn't bother with AppleCare - no issues after 18 months.
I don't generally buy extended warranties for anything - one exception I made recently was the LCD TV we got for my parents. They offered total replacement, on-site, for 4 years, for $200. Since LCD TVs aren't generally fixable, this seemed like a good idea for my parents, who are in their 80s. For us - wouldn't bother.
So...it's highly dependent on your own circumstances/tolerances. If you are willing to take the chance (however small) of an expensive repair out of pocket then forgo the warranty. If you would be incredibly regretful if something happened and you didn't have coverage, then get the extended warranty.
Do have a look to make sure that there aren't a whole lot of reported issues with this model too (Apple forums would be a good place to look).