I enjoy TAS. And I agree with a number of the other people here. I won't go into great detal, since that's already been done better than I would have, I think, but just to voice my support:
TAS has a few truly great episodes (especially the aforementioned Yesteryear), some cringe-worthy episodes, and some solidly mediocre episodes. In that way, it's much like TOS, although the GREAT to CRINGE-INDUCING ratio isn't the same.
My kids enjoy it, though. It's actually been their introduction to Trek, and they ask to watch it. (My kids are 8 and under.) Because of that show, my wife has to endure my son saying, "I'm Captain Kirk! You're Nurse Chapel! You're Uhura! And you're -- Daddy, what was that cat person again?" (I have one son and three daughters.)
(Then again, my kids are also probably the only kids in America who watch Battle of the Planets on a semi-regular basis. What can I say? We don't have cable . . .)
Canon or not? Well, if it is . . . that means there's a six-story tall Spock out there somewhere.

But think about THAT for a moment: THAT'S the Star Trek story Walter Koenig chose to tell when he had his first chance! (Koenig's comic book was better; speaking of comics, though, Goerge Takai's chance at a Trek comic is AWESOME!)
If nothing else, it's a piece of Trek history. Fortunately, it's an enjoyable piece of Trek history. Even the bad stuff.
~ Ben