Hi Nate. Rhino 4 is pretty crazy, it's so far ahead of version 3 that i would hate to be without it. Plus they've already got experimental tools available for Rhino 4 that you can download from the Rhino 4 Labs page... Your head's probably gonna explode when you see what's in the works for Rhino 5. They leak some previews every now and then on the newsgroup and it's just awesome what they're working on in the non-public Rhino builds. I won't spill the beans here, that's for McNeel to do when the time is right. But for now, Rhino 4 is a really productive work environment... I've highlighted some of the major advancements in a thread a few weeks ago (things that are not all shown in the videos)...
http://forums.polyloop.net/misc-disc...rhino-4-a.html
shorty
P.S. - Another thing never mentioned by McNeel but appeared in the last beta is preselection of edges and faces. While in a shade mode with visible isocurves, you can press CTRL+SHIFT+LMB to select an edge or face. Not all commands can use the pre-selection yet, but i have a fair idea of where this might be heading inthe near future...