That may be a hard question to answer, as 7200 rpm hard drives were only an apple installed option on mini servers until now.
In general, you should notice faster boot up times on a 7200 rpm hard drive and quicker responses in disc intensive applications or tasks.
I've noticed more vibration after installing 7200 rpm drives in notebooks, since they're spinning faster. But my knowledge may be stale, and new drives may not have this problem.
I'm almost surprised beyond words that apple finally allowed this as an option on the mini!