Matt Croyden has some good info:

We got the OBD-2 connection to work on my car this evening.  We plugging an old P75 laptop into my 98 Golf, and whadda you know, the check engine light was due to a misfire in Cyl 2 a few days ago.  (I remember it now, I went into second right after starting the car while going up the hill, it was a mistake)  Mike cleared the error, we ran diagnostics again, error gone.

I'm glad I didn't have to pay the dealer to find that out.

Very cool - I'll have to look into that!