I don't understand Berlins appeal. It has one fatal flaw: no industry. In my opinion the great parts of Germany are where the world-famous "Mittelstand" sits. Is that in Berlin? I would argue it's not. Berlin is called "the city of students, the unemployed and cab drivers" by many, and probably not without reason.
Berlin is our hipster-central. However German engineers much prefer the living standards of Bavaria or BW instead of getting their Audi/BMW/Merc torched and their property vandalized. You're not getting lots of these people to move to Berlin. Big (US) IT corps know this, almost all of them have their headquarters in the south.
Now, if you're after 20somethings with no family, low income expectations and you build webapps using $WhateverIsCoolOnHN that targets other 20somethings around the globe - sure, go to Berlin. But then why don't you start wherever you are and get going instead of looking for another excuse that delays your product?
If your business plan even remotely involves selling goods or services to companies, you've chosen the wrong spot of Germany. The same is true for finances, Berlin is constantly broke and banks cling on to their money for obvious reasons.
And if your business plan involves pushing lots of data, you should be in Frankfurt.