Good news: Thanks for saving me the trouble of writing pretty much the exactly same email.
Bad news: I haven't got a solution for you - yet at least
I've played with Arduino Uno so far without any problems and received my Arduino Nano from Dealextreme today. Did a couple of tests with it, everything seemed to work fine, but after a while I managed to get it into exactly the same state you described, apart from the fact that the RX led seems to lit a bit when doing the upload, but it fails the same way nevertheless.
The program I wrote before and uploaded still works, but I can't seem to get anything uploaded there anymore. I've tried pressing the reset button on all the possible combinations before and after pressing the upload command from the IDE, but always with same results.
Is the nano a goner or is there any way of reprogramming it? I know ISP might be a solution, but since I don't know how exactly those work with Nano, would it mean I had to solder out the chip for that or what?
Likewise working with Mac and latest OSX Lion. No luck with two separate laptops. The uno still works nicely though, so probably my usb/serial is still okay.