I have my 2.0 unopened here, and I think I decided to keep it instead of returning it for an MBP. If I bring it back to the Apple Store, can I just pay the difference of the 2.4 MB? How does it work? I am a student, so would I just pay difference of the 2.0 MB + tax and the 2.4 MB and tax? Because that would only cost me around $270. Thanks guys!