http://www.cycling74.com/downloads/max5

Includes over 120 fixes and enhancements, described here:

http://www.cycling74.com/version/version_5_0_6.html

One issue worth mentioning is that if you save coll data in a patcher with 5.0.6, prior versions of Max 5 will not be able to read the data. So if you share colls in patchers with friends, get them to update!