OldSpooky: Could you have lived with the keyboard if the power supply was silent? I don't think I heard others on the DELL support forums complain about a rattling keyboard.
I'm afraid not. My neighbor got a T23 a couple days after I got my D600. Now the T23's keyboard isn't all that great, but after using it, I knew that the D600's keyboard was just subpar. I typed a lot as an undergraduate, and I'll be typing a lot for the next few years of school. I needed a machine with the finest quality keyboard available.
I did find a hack for fixing the D600's keyboard, but I dont' know how well it actually works. The solution is to take out the keyboard and tape foam strips (about as thick as a penny) onto the metal plate (part of the D600 chasis that houses the optical bay). This is supposed to firm up the keyboard considerably.
However, I was not sure how this would affect the internal airflow and if this would violate warranty or not, so I was unwilling to go forward with it. Not to mention that removing the keybooard in the Dell system seems more of a delicate operation than removing the keyboard in the ThinkPad.
Another thing to keep in mind is that the Hard Drive enclosure on the D600 gets very warm. I had the 5400 RPM HDD and it was noticeable. I did not find annoying at all, but many people on the Dell support boards were very unhappy that the heat from the HDD seemed to channel up through the left palmrest.