If and when the Hero allows apps to be stored on the sd card rather than internal memory, then yes. For now, mostly you just have pics and music stored on the sd card so when accessing either you would see a difference in load times. However, most of the lag reported has been related to the operations in the basic OS, which is on the internal memory so placing a class 6 vs the (prob class 2 which came with the phone) will not make any difference. I have a 16 GB class 6 and it produced a noticeable improvement in loading/accessing music and pics, so it was worth it for me.
