To the Mods: Please, can we have a straight forwards 'help me decide on MF' FAQ pin'ed to the forum? There are a lot of them, and they all require the same info (see below).
To the OP: Welcome,
1) What do you shoot?
2) What do you currently shoot with? (D3, but what lenses?)
3) How do you shoot it? (tripod, hand held, natural light, strobes, constant light, street, middle of the night, ...)
4) Are you shooting for yourself or as a paying gig?
5) What do you feel is limiting about your current setup?
6) What are you doing with the images after you hit the shutter?
7) What budget are you trying to stay within?
Where in the world are you?
I would actually start by saying you need to find a local dealer and literally shoot something with a MF camera, take those files and do something with them. For that matter, you may want to start with a CCD based image and see if you even like the output color. The auction was for a film based unit, but are you sure that you want that capability & limitation (bodies that can work with analog film tend to have less integration between the body and the back).
The MF space is wide open, and the used market has so many options, but it comes down to what you want most out of a camera. For example, if you're looking for all weather shooting, I'd say look at the Pentax 645D due to it having better seals, while I'd say a Phase One setup is going to make a landscape photographer happier as it can be used on technical cameras and bodies without tethering.
This is where in the world you are matters, as dealership and rental options can help, as can meeting another photographer in your local area who has something you are considering.
Personally I'm a H4D user. I love it, it does what I need, but I'm also Phase One Certified. The one thing I will say is that MF/DMF will cost you more than you expect, so please be really clear as to what you are looking to accomplish.