I bought the 340mb microdrive and ultimately also a 1GB. The 340 had intermittent problems and I lost a TON of shots before I figured out it was the Microdrive. BEWARE they are known to be flaky.
The 1gb drive works well. I always shoot raw files which are around 3.7 mb each. I can get about 245 pics at raw resolution on my D1 which is really nice. However, the 1GB drive is slow. When I shoot rapid shots, it only buffers I think 10? before it slows down to a crawl and takes 20-30 sec? to save each one before I can shoot again.
If the solid state memory cards come down in price, I would go with them because of reliability and SPEED.