I don't think the game population will double in two days since anyone who is playing in two days is probably playing now. I think a week or so from now when sales in stores probably pick-up is when you will see a large increase in players. So you probably have at least until Friday before the server collapses under it's own gravity and forms a black hole.
Well considering the condition of the roads around were i live today and into tomarrow.. i likely whont be getting my copy of the game till probably wensday or thursday... but beyond that?... the game is going to be just like it is now.. only instead of haveing to wait 20 minuts to get past the 'gathering character list' messge... you'll spend 45 minuts, Rather than waiting 10 minuts to 'load' into the next area, you'll spend 20 minuts.
oh.. and there will be a 200% increase in the number of "were's Sulu?" questions in chat.... the 1 and only 'war-zone' map will STILL be busted...
about the only thing that'll change for the 'better' is we'll actualy have our pre-order goodies..... now if only we could play with them after we get them... :p