The only way you'd notice it being a bottle neck, would be if you had it on a SATAIII connection first and moved to a SATAII. It will be an improvement on a mechanical HDD even on SATAII, for sure. And you can always move it to a new build with SATAIII when you upgrade.
Thanks for the info, clutchc! I do plan to upgrade to SATA III eventally. School is sucking up all my money at the moment.