Nope, I've taken it out straight after taking several dozen shots in a row, and it's never more than slightly warm. Plus it doesn't void the Nikon warranty, it's just they don't guarantee compatibility. This is mostly due to the problem with the orginal Microdrives that revolved at 5400rpm. The newer MarkII models run at 4200rpm I think.
I find start-up time is a couple of seconds longer with the drive in the camera compared to a compactFlash card. Also some operations like viewing thumbnails takes slightly longer. For my uses it doesn't worry me, I enjoy the freedom of being able to take 670+ pics at max res, minimum compression settings. In fact I would empty my three rechargeables before I hit that amount of photos. If I needed 5 shots per second, I would have got a Nikon D1H
