I recently encountered an issue at a client where their Exchange Server 2010 Database Availability Group, which spans two datacenters, would fail [all databases would end up dismounted] when the WAN link connecting the sites saturated. The simple fix was to heed the Exchange product team's advice and apply a hotfix written to address issues like this. Please see below for a link to the EHLO blog post announcing the fix.
http://blogs.technet.com/b/exchange/archive/2011/11/20/recommended-windows-hotfix-for-database-availability-groups-running-windows-server-2008-r2.aspx
Matt