Went there last night for the first time and it was a really nice little place. It's name is spot on because it is very easy to miss in it's hidden location on a slightly obsure street. The Hidden Vine is in a basement location that you enter from Cosmo Place (same street as Le Colonial). There is a small awnig that simply says "wine bar". I believe there is an entrance from post street too, but I didn't see it myself.
The place itself is very cozy. Kind of a dark room with a variety of couchy seats, tables and a high-top with stools. There is also a small, 4-stool bar. They have a long list of wines by the bottle and many by the glass. We went for the flights, which they do a great job of putting together. I had the cal-ital flight, 3 reds that are made in California with Italian varietals. Big thumbs up on the 2003 Gianni Paoletti Nero d'Avola, Napa Valley. My wife had a white flight called "fun & funky" which featured less common California whites. They offer comparisson tastings too, like two pinot noirs from different regions; I'll go back to play with those. Oh, and the staff was very knowledgeable about the wines and friendly. They gave us some great info and had answers for all our questions, they really know there stuff!
They also offer a nice selection of local cheeses, sausages, olives, and xox truffles.
For a pre or post theater stop, or just a glass of great wine and a light snack this place is great.
620 Post St, San Francisco, CA 94109