I definitely recommend AppleCare for laptops and iMacs. They both are relatively difficult to open (especially the newer iMacs which require screen removal for everything but RAM swap), and 99% of the parts used within are proprietary Apple. Lose a screen or a motherboard and AppleCare becomes a VERY cheap investment.
For the MacPro machines, it may not turn out to be a guaranteed win but, over time, it’s likely worth it.
For the iPhone it’s a different animal. They do cover quite a bit, but nothing accidental, etc. This is the one device where I’m 50/50 on it (or, if you look at my purchases, 33/66 given that I’ve purchased—and used—AppleCare on only one of my 3 iPhones).
The most important thing to remember here is that Apple’s entire support infrastructure is build around you having AppleCare. Without it, support becomes a much more cumbersome—and often disappointing—process. The lone exception to this is the Genius Bar where oftentimes Apple’s obsession with customer service results in Geniuses that will go above and beyond for someone who doesn’t have a warranty (this is a good thing, of course). Still, if you have significant problems with your machine, your AppleCare status is often the tipping point if you ever have to call Customer Relations to see about a machine replacement or some such.
In short, I do recommend it for Laptops and iMacs, I’m on the fence with iPhones and Mac Pros (and Mac Minis, simply because they’re so cheap to begin with).