About a week ago Stylish Corpse put up this nice post about PQs and Grouping in MMOs in particular. As I haven't played WAR I cannot comment on PQs.
However I do disagree with some of the blanket assertions used by Stylish Corpse regarding Grouping and leveling and I can comment specifically about WoW.
"if you do want to group you have to put up with getting less xp, taking longer to complete quests, and generally getting less bang for your questing buck than if you were by yourself."
S.C.'s main point is that questing alone in MMOs today is better in the XP/hour department and therefore discourages grouping. I agree with this, at least in general. However, it's not so black-n-white, for example there are always group quests in every area of WoW and you'll nearly always see players writing in /1 asking for a group for that. I admit the mechanic for looking for a group for these quests could be improved but the point is such quests do exist and people do find groups for them (I know I have) - so it is not like questing at least in WoW is 100% solo. I suspect the same is true of other MMOs.
"What I would like for the next few MMOs to do is to provide some genuine benefit to grouping..."
Well here's the funny thing, WoW really does have a genuine benifit to grouping. The XP/hour, gear upgrades and everything are really good there. Only it is not for questing, it is when using the LFD tool.
Making this tool cross-server and allowing you to do any instance in your level range randomly however many times you wanted per day has had a huge influence on leveling. I would estimate my Warlock gained about 70% of his XP while leveling from instance runs and this was mostly because I had to wait so long as a DPS (~30 minutes) between runs. Had I been a healer or tank I suspect 90% would have come from them!
The XP/hour is amazing, I would be questing along for 20-30 minutes doing about 1/4 or less of my bar to next level, then the LFG window would come up and in a short 20 minute run I would be doing 1/2 of my bar to the next level. Not to mention gear drops!
I guess you have to experience it for yourself to realize what a difference the new LFD tool has made for leveling. I know I underestimated its effect by a lot before leveling my Warlock to 80.