Hello Xsiers,
I been using Zbrush latelly for all my modelling work.
i create a simple mesh in XSI, then export it as .OBJ to ZBRUSH and in there i can go crazy on details, then i can use the detailed mesh as a proxy for rendering and texturing and keep the low one to animate.
There is also a very nice method to use the detail created in ZBRUSH as a displacement map in a low res mesh, but that workflow i didnt get right yet.
Heres a head i did in xsi as low poly and then detailed in ZBRUSH:

and heres an arm. again i did it with less than 200 polys in xsi and then detailed it in ZBRUSH

I just wanted to share with ya guys this workflow that is helping me a lot.
cheers
L_