I agree with Simon. Stick with version 6 for now, but do keep up with the patches issued since the 6.303 install CD release. Version 6.311 is where you should be today.
Yep, do what Simon and VelvetFog say! We have 6 ASL machines, all running 6.311 (ok, one is still on 6.304, haven't had time to schedule brief downtime for the updates yet).
We are doing some light testing of v7 internally but there is still too many trouble reports for us to seriously consider upgrading any production sites to it yet.