The biggest change in this release was the upgrade of the old Samba 3.0.x package with the latest from the Samba 3 series (3.6.24). Note that while this might introduce a slight decrease in SMB throughput on some models, it should overall help with the interoperability with various SMB clients, and general security.
Thanks for this nice update. I updated my N66U from latest official firmware to your 376.48_3 and the funny thing is: My SMB speed increased from 8 MByte to 12 MByte / second. That's amazing, thank you.