could you go into why tag aware sharding is a "HELL YES" for you? I was kindof already of the opinion that mongo sharding is much too complicated (http://i.imgur.com/c3Dpq.jpg), this seems to compound that. Is it something you've needed/wanted so bad that its worth it?
notes summary:
• Aggregation Framework to fix some map-reduce woes.
• TTL Collections
• DB Level Locking (A step in the right direction)
• Better yielding on page faults
• Tag aware sharding (HELL YES)
• Better Read Prefs
• Indexes now handled by mongodump/mongorestore
• mongooplog replay is awesome for getting point in time backups
• Shell now has full unicode, multiline command history, $EDITOR support (all from change to linenoise.c