After using Messages Beta for a week, I ended up uninstalling it. Kept getting a red badge "1" on the dock icon that wouldn't go away.
The worst bug in iMessages was this nasty problem that ended up eating ALL available boot disk space, as widely reported in the Apple Support Forums.
Once this happened to me, I uninstalled the beta release and got back to iChat with no problems so far. Hope this is sorted out before official release in July.