I always get it. I have two white MBs and a Mini (one is my wifes), which have had the following replaced, free, usually within a day:
the keyboard (3 of them - 2 on my laptop, 1 on my wifes)
bottom case (both laptops)
top case (same)
bezel (same)
(usual cracking issues around the hinges etc, and the rest were just a bit worn),
the fans (in 3 hours - seriously, the turn around at the Regent St apple store in the UK is _fantastic_),
and because I had three macs under warranty (ok, maybe not _because_ of that, 1 would do), they replaced my TimeCap 500GB with a 1TB when it went t-s up. I didn't get my data off it, but other than that....
I think it's worth it. for every day I'm without my macbook (soon to be a pro this weekend), it costs me around £400, not to mention the slipping of deadlines.
So I can make the cost of the apple care back in around 3 hours. £180 for the warranty is worth it. I've gotten back 2-3x that just in the repairs. Keep in mind I'm VERY VERY careful with my laptop. Most of the time, it sits on a stand next to my desk. No chance of coffee or anything getting in etc. It's a little more dusty than I'd like, but noone could claim it was "dirty"...
I'm only replacing my MB (2ghz, 4GB, 500GB) for two reasons: it's almost out of the 3 year warranty, and I can't get 8GB in the thing to run enough VMs. Other than that....
Well that's good that you feel you are getting a lot of value out of it. Some people never try to cash in on the little things like free replacements for wear. These things are always a judgment call, and what you are really buying is piece of mind. I do challenge you to consider going forward whether you could have managed these repairs yourself or by paying someone per job with the $647 that you spent on Apple Care across these three products. It sounds like a lot of your repairs were for problems that were the result of general wear and tear and weren't actually preventing the use of your laptop. It might be nice to have that $647 to put towards your next computer purchase instead... just food for thought.