I use also Mac OS X Lion 10.7.2 with TeXShop 3.06 and everything works perfectly, both mkii and mkiv from the Minimals (everything is also fine when invoking context from the command line in Terminal). However I never succeeded using mkiv from TeXLive?
Maybe you could say how you typeset your files in ConTeXt?
I use TeXShop 2.43 (which, incidentally, tells me, when I check for updates, that it is the newest version available.) with an engine that reads:
#!/bin/bash
source /Users/robertblackstone/context-minimal-04-11/tex/setuptex