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RE: East Berlin advice
I stayed in East Berlin last summer, like you, I wanted the East just because of the historical reason. Plus I wanted something with a good access to pubs and stuff for the night and some friends refered me to Friedrichshain area. I also wanted to be close to the metro station for quick access around the city.
What I found was the U5 metro wasn't the greatest as I pretty much always had to connect into central Berlin to go to other parts, or take the long Ring S-Bahn around the city. Also I didn't find too much of intererst in that area of town either. There was some night clubs, but no real good pubs or anything that I found. The hotel I had there was pretty bad, not because of the room, just because of how the hotel was run and that of course isn't anything to do with the area of town, but Hotel Pension Bolgerini Inn I wouldn't recommend at all.
If I go back, I'd probably chose another area in the former East Berlin to stay at and avoid at least that area of Friedrichshain near the S-Bahn as there just really isn't much there to do that I found, and connections to the rest of the city wasn't the greatest by metro either using the U-5.
If you can find areas closer to the center that are still in East Berlin, I'd definately opt for that or at least something closer to the U-1 or U-5 metro lines...