Just today I returned from a week in Berlin, I go for work a couple of times a year. It's an amazing city for bikes, paths everywhere, bike specific traffic lights, and most drivers are aware and courteous (if you follow the rules). Most people ride city bikes, dutch bikes, mountain bikes, cheap department store bikes, flea market junk, etc. Lots of practical stuff attached like baskets, bags, trailers for kids and so on.
Fixed gears were pretty rare until recently and this visit I saw more than ever. It's definitely on the radar and it doesn't surprise me at all that the cops are forcing people to install brakes. While Berlin is one of the most liberal cities in Germany, they are still relatively strict regarding vehicle safety, like the rest of the country.
Bonus material, I went to this small new (well new to me at least) bike shop in Prenzlauerberg called Rembetis. Shop owner was a really nice old dude, definitely a life long cycling fanatic and absolutely knows his stuff. He used to set up in a nearby flea market and do repairs and sell used parts, etc. Had a nice conversation and he showed me some of the old 50s and 60s frames he was reconditioning. There were some really sweet vintage track bikes on the wall. Prices were reasonable, starting at 400 euro (US$566) or so for some quality classic builds. Anyway, check him out if your'e ever in Berlin:
http://www.rembetis1.de/index.php?id=17