I've lived in Beijing for almost two years, and there are lots of things to do there. I just came home stateside for the next few weeks, though, so here are a few tips:
There is a very vibrant gay scene, albeit concentrated around one spot called Destination on Gongti Xilu. It's very crowded and mostly Chinese. There is a really classy and nice gay night on Thursdays at Mesh, the bar of The Opposite House Hotel on Sanlitun Beilu, frequented by the expat community. There's a new gay venue apparently but I haven't heard much about it (like name, place, vibe).
As for hidden gems, you need to walk around the hutong and the Siheyuan near Houhai and Beihai. They're really beautiful, and in the process of disappearing.
The best part of the Great Wall is Simatai. Last I knew it was under renovation, but the section next to it is still open and nearly as breathtaking, called Jinshanling. You can arrange a driver to take you from Beijing there and back for around 500-600 kuai (renminbi). Bring warm clothes because it's COLD right now.
The 798 Art District, especially the UCCA, is a must-see if you like art, especially modern art.
To go Alameda for lunch during the week, it's exquisite, on Sanlitun Beilu, but look online for the precise address because it's kind of down an alley and around a corner, if you don't have help finding it you might not.
Get a drink at Apothecary in the Nali Patio, Sanlitun Beilu, 3rd floor, they have the most amazing cocktails in the city. Sanlitun Nanlu also has a nice cozy place called the Bookworm with good jazz and wine on Friday nights until 11.
Go for Peking Duck at Dadong or Quanjude. Both are very tasty, and Peking Duck is something you must try while in Beijing.
Gee I'm having trouble thinking of everything worth doing! Beijing is a city that always has something going on, so pick up Time Out of The Beijinger or Agenda (they're all free and you can get them almost anywhere) to find out what's on the calendar. If you have any questions, feel free to ask!