I've had mine about 3 weeks now, I think, and I've got to say I love it. I've had no issues with it *knock on wood* and I appreciate the much needed space. I've noticed no difference in sound, vibration, heat, or anything else compared to the drive it shipped with (320G Hitachi @ 7200RPM). No change in battery consumption either, since I had a 7200RPM before; but I've played with a 5400RPM drive in it, too, and noticed no real difference in battery consumption there either.
Honestly, the only difference I can tell is that I have more space. I used SuperDuper to copy everything over to it and after I installed the new drive, it continues to work as flawlessly as it did before. I recommend it if you need the extra space like I did.