The 5400/7200 rpm difference isn't noticeble for every user. It all depends on what you use the HD for. If you use it to store your mp3s, play a few games, some amateur programming, e-mail, etc, then the rpm difference is negligeble. If, on the other hand, you work with Photoshop or 3D modeling a lot, you visit gaming news sites more than 12 times a day, or you actually run a server, 7200rpm is a minimum.
Vlad