This one is hard to tell with out Bioware / EA tell us, so i’m going to make an educated guess from, the data i see.
My source of data are
Torstatus.net and swtorarena.com are both based off Server populations. Problem with this is if Bioware changes the definition of how many players heavy, full, light are, the statistics change. Both side show that the number of Full server has dropped from about 20% to almost 0%. At the same time light server have gone from 25-30% to about 40% of the server. IF bioware has not may server improvement this would point to a loss of player (of about 15-20%, from the peak).
Now Xfire numbers are different. Xfire reports on the number of hours the game has been play by the people who have xfire installed. This number on the other hand is roughly even, which would mean bioware number 3 weeks in are roughly the same as they were at launch.
An interesting side note if we look at Xfire number for WOW http://beta.xfire.com/games/wow WOW only has 1/3 more hour play this week than SWTOR. And also twice the population. So that actually pretty good.
Now the big question is what happens 1-2 weeks from now when people move off their free month of the game and start having to pay. I am assuming there will be a drop, it hard to tell right now how big.