I've got a '92 SE and this morning when I cranked her up, there was a thump-ish sound (sounded like it was from directly under me, maybe towards the passenger side a little). It wasn't loud, but having started my Bonne thousands of times, I noticed that it wasn't usual. Then, when I try to accelerate (even in reverse) the car kinda jerks as though the acceleration goes out for a split second and then comes back. However, after a few rounds around the block and some heavy acceleration, it seemed to go away. I drove for probably about 100 miles today and everything seemed ok, but I'm worried it'll happen again. Anyone know what the problem could be?

Might have been a motor or transmission mount. I don't think anyone can tell you postively what made a thump under the car..lol

Was a cat or snake in your motor to get warm?

I actually thought about this, and I certainly hope there wasn't. I did check under the hood, and everything looked ok. And I looked under the car and didn't see anything.

Pop the hood..get a helper. Stand them off to the side of the car. Put it in gear and give it a little gas. Does the motor move like a bad mount?

That sounds similar to what my wife'* Grand Prix was doing a couple weeks ago, If I opened up the throttle it would make a popping noise from underneath the car, and hesitate and not accellerate. It turned out to be a plugged catalytic converter. Apparently federal law requires the manufacturer to warrant it for 80,000 miles or 8 years, and in California it might even be longer, like 100,000 miles and 10 years.

This may or may not be your problem, but you can see if you can repro it by going WOT on the highway.