Probably until about 6 months after Civ 5 comes out - so until March next year, I guess. I never buy new release games. I wait until (a) several patches have come out and fixed the major issues with the game*, and (b) the price point has dropped.
* no matter how good your beta team is, they can't replicate the issue-finding power of tens of thousands of players, particularly with a game as rich and layered as Civ
* no matter how good your beta team is, they can't replicate the issue-finding power of tens of thousands of players, particularly with a game as rich and layered as Civ