Definitely, unless you are prepared to spend 1k+ on repair parts such as a logic board, cpus, etc... on a mac pro sure you can replace the cpu, hd, optical, or ram if they crap out but the logic board and psu are costly to replace, so your choice to weight out the pros and cons
On a laptop it is a must.
This is my personal experience with applecare:
My 17" macbook pro for example, applecare was ~$300 (ebay), since late march I have had replaced: battery (~179), then main logic board (~1k), then topcase (~700), and now my trackpad button is bunk... they are now replacing it with a new unibody 17

(should get the 2.66, they're calling me tomorrow to work out the exact specs as my 17 was CTO so they have to try to match it as close as possible), so that makes my $300 investment more than worth it.
On the other hand, my ibook never had applecare and has not had any issues aside from the airport card crapping out, so in my experience, it can go either way but is worth it
IF soemthing goes awry.