I own a Nikon D90 and bought the MC-DC2 through Amazon. The MC-DC2 plugs into the D90's GPS slot. Very easy to use after that - you press the release button slightly to autofocus, and press it completely for taking a picture. It cant get simpler than that! It therefore supports all modes of operation - single, continuous and bulb (for long exposures).
In my view, the MC-DC2 is overpriced. You might want to check out its equivalents, or, the Hama NI-3, a radio control with a range of about 30m. See Hama 00005369 NI-3 Wireless Remote Control Release for Nikon Camera
. Since it works on radio, it is not limited to line of sight operations (like the rather silly ML-L3 remote - see Nikon ML-L3 Remote Control
). I have both the MC-DC2 and the Hama because the latter needs batteries, and the MC-DC2 does not. So it is a backup, should I run out of batteries!