To me, it's the queuing system and UI. The ability to queue anywhere is one of the best things Champions Online does with their PvP system, and Turbine, you guys need to rip it off wholesale. It allows players to get in and get out, and quickly get back to what they were doing. Taverns are nice, but as much as they should be, they're not social areas, and people aren't going to wait around to queue for a match when they could be out actually doing something. In my opinion, that is what kills PvP in this game.
If the accessibility were there, more people would do it. I'm not a programmer, but it seems like setting up a worldwide queue system should be a relatively simple thing to do. PvP in DDO sounds fun in theory, but I have yet to actually try it because of a simple problem, and I really feel like I'm missing out on something fun.
It's sad that there are less than ten threads in the PvP board. EU is a big opportunity and I don't want a lack of PvP options to turn players away from this really cool game.
This is just my observation. Does anyone else have any ideas about how to make PvP better/more popular?