IMO only revolution or total banks crash could force average "normal" people to commonly use bitcoin. Without that it will be interesting thing for some geeks and blackmarketers.
Bitcoin ~= Linux imo. In all the visible markets it'll just be its own dedicated group of hippies - even in a revolution normal people will just stockpile gold, guns and food first - but slowly and quietly it will take over more professional markets like international money transfer and financial applications one by one, and in 15 years' time we'll all be using Bitcoin without even realizing it.