I went to a work retreat in Napa last fall, and we had a lot of fun. We did a sweet bike tour that included tastings at four vinyards. I don't recall who the tour was with, but it was a pretty sweet way to go.
Don't miss Robert Sinskey, Stag's Leap, and Clos du Val. One of my favorite wines from that trip was by Miner, although we didn't visit the winery.
Have fun. Napa is a good time.