You were still kinda vague on a few things, but I think you get the general idea. I'm going to go a bit farther and suggest a few specifics.....
If you just want to go and hang out - pick any coffee shop in the Castro and on Market St. Starbucks in the Castro, as well as Tully's & Spike's. There's Peet's on Market and any of the little restaurants in and around the area.
There's also Cafe Flore on Market/Noe/16th, Bagdad Cafe, and the Squat & Gobble restaurants if you again, just want to hang, meet people, or people watch. If you want quiet and community, head down Noe to Jumpin' Java (and most have free WiFi so you can do work as well). Don't forget your power cord. If you continue up Noe, you'll hit Duboce Park (fka "Dogshit Park") and you can people watch and let your dog run and play. You can also catch the N Judah and head downtown on Muni. If you go into the opposite direction, go thru the tunnel and get off, you'll be within a few walking blocks of the Haight and some incredible wine bars.
If you enjoy the bar scene, pick one as there are plenty in the Castro & on Market - I think the newest is called "Trigger" on Market next door to Streetlight Records.
Another thought is to wait for the annual street fairs - the Castro Street Fair is huge and encompasses most of the places I've named here. The guys have also shared url's with you for more spots.
Enjoy & Happy New Year!