Hi Chia,
Long time no see. Good to see you back here.
If my feedback counts, I have it in one of my nonprod/test environment (got last week only) and so far it's behaving but environment I have is fairly simple and straight forward (one master configured as media server too with a tape library, no disks, which means not using any of the cool new features). Given the addition functionality 6.5 have, I would say plan to move on 6.5 instead of 6. It is due for GA sometime in August.
If your environment is fairly large, Symantec has special program for doing upgrade for you. Contact your sales rep.