***UPDATED*** - 6/19/2013
As part of the Lync 2013/W15 TAP program with Microsoft, we were one of the first organizations to deploy Lync 2013 into production. In doing so, we also had the joy of experiencing the migration "gotchas" before deploying Lync 2013 into customers' environments. One oddity I ran into when performing the Edge migration from Lync 2010 to Lync 2013 was with our Lync Online federation partnerships. Post-migration, many of these federations flat-out broke, and others that seemed to work were behaving strangely. After looking over the errors and symptoms, we got everything sorted out - and the solution was relatively simple. However, I'm still unsure as to why this issue was allowed to occur in the first place.