Thanks again everyone for your stories- everyone who has made any progress in their splits should be considered an inspiration, and proof that flexibility can get better, even if you can't always see it when it's happening.
@Legend - Don't get too frustrated! Right now I figure it might be another year until I have a real split. That's OK: one thing I learned from my dad, who was a marathoner, is that getting into the best shape your body can be in is also a psychological task; you need to keep your eye on the long term or you will burn out and give up.
It took me a long time to apply this wisdom to the splits, and realize that part of the problem is the psych-out factor. Few things feel worse than being in a dance class when everyone else goes down in the splits, and you're so far off the floor you're just trying to balance somehow! I seriously started about 18 inches off the floor. It also took me a long time to realize that a big reason I never really tried to get my splits until recently was the fact that I had to overcome my own negative feelings about the limits of my flexibility in order to face practicing regularly first. Unfortunately, when I did start to practice the splits, at first I pushed myself too far- blaming myself for not having my splits because I wasn't working hard enough- and then had to take time off to recover. What an excercise in frustration!
I may not be in the splits yet, but what I've learned along my journey, besides the psychological stuff is the following:
1) If you're working hard and are in pain, but not seeing results, you may be working too hard rather than not hard enough.
2) Using a foam roller first helps a lot (I have a lot of adhesions in my leg muscles from running for years without stretching), especially for those of us who can't afford a masseuse.
3) Make sure you're really, really warm. I found out the hard way that a "normal" warm-up doesn't cut it for me. I either have to run like two miles first, or if I don't have time for that I take a very hot bath.
4) I was told by an instructor to try doing my splits on top of a bolster or pillows, and this reduced the pain by at least 50%. And yes, I have made progress doing it this way.
and
5) You have the rest of your natural life to get into the splits! It will come in time. In the meantime, relax and don't hurt yourself. :)