The official release forum thread which contains the standard celebration and thanks can be viewed at: http://codeigniter.com/forums/viewthread/70329/P15. So far the most interesting posts for me are from PoWah and tonanbarbarian which indicate a small increase in overhead and speed but nothing serious considering the additions.
Some 1.6 specific bugs have been trickling in on the bug report forum but I haven’t seen anything major as of yet. Most issues in the CI Bug Tracker were dealt with in this release so it is looking very clean.
As with previous CI releases there are few concerns with backwards compatibility. Further, Derek Allard, one of the CI developers has basically stated that it is fair to ‘expect tighter development cycles’ and that they already have 1.6.1 code.
If you don’t know what CodeIgniter is or haven’t tried it, I highly recommend it. In my opinion it is one of the top PHP Frameworks with boasting rights in speed, simplicity, documentation and community support. You should have no trouble in knowing what works in various versions and if you understand PHP you shouldn’t expect any serious learning curves.