Well I haven't used one before but I've read that they use them in CAD and scientific stuff for viewing models. I've never heard of them being used for modelling (don't even know if its possible) although I think that thier precision rotating and zoom feautres would probaly be useful for manipulating shapes that are organic.

By the way have you heard of that 3D sculpting pen tool? I saw a documentary on TV about how they reconstructed a mummified person's face from MRI scans with Zbrush and the artist used it to sculpt the model. I think that would be more suited to modelling although I have no idea how much it costs.