[ignasl]

Probably Berlin. Vilnius or Tallinn could be interesting choices because of friendly business climate, lower taxes, competent and cheap talent, not far away, good tech culture and basically 0% chance that someone would try to outlaw your business (Germany probably has a bit higher chance but I guess it's also not that high). I think US do have some restrictions about exporting encryption to some (all?) foreign countries so you better look closer into that before making a decision. P.S. Stockholm also could be a good place. It's just quite expensive.

[throwawayblwBz]

Vilnius and Tallinn are definitely highly tempting, just from the simplicity of getting set up over there from a business registration standpoint (at least in Tallinn, not quite so sure about Vilnius). There are a few concerns about Russia's attitude to the Baltics, though - probably overblown in the press over here, but we'd need to research.

Berlin - yes, definitely a tempting option.

[threesixandnine]

Very overblown. Almost histerical paranoia. Even people in Vilnius are not so afraid of Russia as people here in the UK.

[KingMob]

There are indeed some restrictions, but nothing like in the 90's. For the most part, as long as you're not exporting to designated "rogue" states, it's just a matter of some licenses and occasional reviews, though IANAL.