I've been flying the MD-88 for almost 12 years now. I think it handles fine at high altitudes. It's more pitch sensitive at the higher altitudes. Like someone else said, you have to constantly make a lot of small, delicate control inputs... you can't just trim it up and let go for any length of time. The thin wing is definitely a problem on that airplane, and maintaining an appropriate cruise speed is critical.

I found the handling at high altitudes to be about the same with the B-727 and the DC-9. A little pitch sensitive... but not nearly as bad as the Jetstream 32 I flew years ago!