This is the first long term support release of Asterisk since version 1.4.0 was released in 2006, and there's >200 notable new features. A few important features that stuck out to me were Google Talk & Voice support, improvements to SIP handling, calendaring integration, and less noise on conference calls. For a good writeup of some of the new features, also see:
http://blog.tmcnet.com/blog/tom-keating/asterisk/asterisk-18...