Hey Lawson, there seem to be more people coming back everyday (or at least new toons getting on and getting added). I've never had a problem doing any of the group content that I've tried to do. The server population is great at any time of day or night. The only thing I can't attest for is the Operations -- I'm inexperienced doing those mainly because I'm an altaholic and am leveling up 14 toons. On-world Heroics, Flashpoints (now with group finder!), and PvP warzones I've never had trouble with. I also find that people on are usually willing to help if you ask, too.
Hope this helps -- see you in game!