We recently upgraded to 7.6 and ran into a few interesting issues. 

1.  We use the Inventory Valuation process to build our BI info.  They've changed this to not use the main temp table anymore.  In our case this presents a pretty big problem due to log size growth.  My solution will likely be to write a new SP and use the old temp table. 

2.  Some of the reports upgraded to the new version of Crystal.  The export options no longer work the same and our staff has had to find workarounds.  Not a biggie but they have one or two additional steps now.

3.  The Aged Receivables report has a bug.  It still works but it reports an error. 

4.  Make sure you check the supported platform matrix.  XP and Win 2003 terminal server are no longer supported.

5.  They've fixed the Receipts Line view to work with Landed Costs.  Glad they fixed this.