I've been playing TOR for about a year now. The merging of servers has been good so far - there are a lot more players in zones now.
The only problem is that you really don't need to group with other players all that often - unless you are doing the Heroic quests. And even then, a duo (with companions) can plow through them with a little effort. Granted, my highest toon is level 27 or 28. Maybe groups are required at higher levels.