Keeping files in sync across multiple computers

Hi there,
Does anyone work with the same files across multiple computers? If so, I need some advice. I work primarily on a PC at work (I know, bummer). I do a lot of travel for work - I use a Mac for that, and a Mac at home. But, I end up working on a bunch of documents, taking them with me, editing them at home or one a laptop, then back at work, etc.

Some caveats:
1. I don't always have a good dial up connection on the road, so I hesitate to use webstorage.
2. I am hoping to not just carry around a hard drive and always work from that.

Sooo, is my best approach just using a little portable USB drive and using that as my primary working hard drive on all the computers?

Any suggestions are welcomed.

THANKS