I'm a young developer living in Germany. Here's my perspective. Berlin is cheap, affordable, has an international culture (I'm an emmigrant) and pretty much something to offer to everyone, so the city itself just has a good attraction for young people.

I don't know why the startup scene has started booming here but just type in "web start-up" at indeed (http://www.indeed.de/Jobs?q=web+start-up&l=berlin) and you'll get 275 results. Plus the UK has cracked down on emmigration laws and Germany has opened them up, at least for engineers, etc. b/c of the "Fachkräftemangel" i.e. the fact that the Germans lack skilled laborers. So whereas before for Europeans and especially Eastern europeans the UK was #1 its now changing b/c Germany is closer and easier. Also Germany seems more open to Europeans period, the UK with Cameron is doing all it can to shun the rest of Europe. The only problem I see, is that you still need to know German to get around ( which no one studies in school), which for instance is why my brother hasn't come.

EDIT: I guess I exaggerated with the "no one studies in school" bit. My point is that english is the only language we are all pounded into learning regardless of whether or not we have an interest in languages or a talent for them, so we can at least function at some level with english. German, however, is not the lingua franca I think we can all agree on that. I'm quadlingual (if that's a word), but not all talented developers like languages as well and unfortunately whatever the germans say, you still need to know german if you want to assimilate in germany, get an apartment, go shopping, and live life.