Great transit links? Not by airplane in my experience. Also, Frankfurt, Hamburg, Munich are closer to other large, rich European cities. Berlin is dreary and, in my opinion, a clusterfuck. Obviously my judgment is clouded by the fact that I don't like Berlin. My girlfriend lives in Berlin and so I spend way more time there than I otherwise would. Don't get me started on Kruezburg.
I wouldn't be so sure. Unless Lufthansa decides to make the new BER a hub (unlikely with FRA and MUC already playing that role) it probably won't see much more transatlantic traffic than it already gets. United already has a nonstop to NYC and I think that's BER's only North American destination. Unless a lot more SF companies open up in Berlin I think they'll just have to make due with the SFO-FRA/MUC nonstops and connect from there.
BER is indeed intended to be a Lufthansa hub, on par with the others you mentioned, at least according to my airtravel-nerd girlfriend - I'd link you if I had the source.
A flag carrier with two major hubs that also operates a non-hub in the shiny new airport in the Bundeshauptstadt? Doesn't make sense to me, either.
Also, presumably the Continental 5-plus-times-a-week TXL-EWR will be moved over to BER when it opens, as well.
