Firstly, you may want to check that you're using a regular version from http://www.sublimetext.com/2
, and not a dev version from http://www.sublimetext.com/dev
. The regular version gets weekly updates, while the dev version often gets daily updates.
There will be a way to stop update notifications when the final version of Sublime Text 2 is released, but it's not high on my priority list to implement for the alpha versions.