Have you considered adding something that automatically updates the client and just requires a client restart to switch into the new version? This is what Google Chrome does and it's incredibly useful for pushing out updates. It would make client updates a lot easier to do, and make this switch from v5 to v6 a lot less "big".
I'm not personally aware of any bugs in v6, but there will (probably) be some found in the future, so I think getting a streamlined update system would be a good move.
Regarding other improvements... well, there is a whole section on the forum for that.
