Griefing may be a big problem in PS2, it was aggravating in the early days of PS1 when it happened and there we had mechanics in place to limit it. Here I've seen no mention yet of how they will deal with it, they've even said it'll be relaxed?
I envision people getting into slugging matches in the spawn areas, people blowing up consoles etc
. In F2P they are going to need very smart ways of dealing with multi account griefers, there are a few but there are ways around these also.
The only one I ever come back to thinking about, is friendly fire damage could be 100/50. If you shoot a friendly, you get 50% of his damage as well as him getting the usual 100% - Aoe is still limited just the same, (its actually limited even more) and you'll die if you go around shooting people on purpose.