There's precious little documentation on this that I can find. I've got as far as getting a new tab to appear in the admin panel, and it seems to have all the right controls, however clicking on "Create" just throws a js error:
processOnDemandHeaders is not defined
which seems to be jQuery related. I'm planning on debugging this further when I get the time, but I'd like to hear if anyone has actually got this to work.
Try checking out the lastest 2.3 branch code (not nightly builds which apparently are not being updated). I finally got this working last night after being told by simon_w that there had been a number of fixes for modeladmin in the last few days.
I have no idea how you guys are getting this to work. I don't see any new tab in the CMS, and when I try to manually enter the url /admin/crm, I get a Fatal Error: Disallowed action "crm" on controller CMSMain.