Decent food in Union Sq. area?????
Walk down to Westfield Center (yes, i know, it's a MALL) and try Out The Door, which is an offshoot Slanted Door - a fancified Vietnamese place that most people seem to think is our city's best restaurant! i disagree, but Out The Door is a different story. Try the pork bahn mi. no, not authentic, but very good nonetheless.
I doubt you'll find many people on Chowhound who'd call that place the city's best restaurant.
There are many decent chow options around Union Sq. This thread comes up at least once a week, so a quick search will turn up the details you'lre looking for. Keep an eye out for
Le Colonial (Vietnamese/French)
Hidden Vine (wine bar w/ light bites)
Belden Lane (mentioned by rworange. B44 & Plouf are good)
Cafe Claude (casual French)
(Also, you're quite close to Chinatown, so search for posts there)