The Daily Grind: Concentration buffs

Over at Kill Ten Rats, Zubon brought up the topic of concentration buffs. For those that don't know, a concentration buff is one that only needs to be cast once and will remain until canceled, and takes up a certain portion of the caster's "concentration" (as a way of limiting the number of perma-buffs that are enabled). Both Dark Age of Camelot and EverQuest II use this system, and there are certain Lord of the Rings Online buffs that only need to be used once -- but why aren't more MMOs making use of this?

Not every buff should use the concentration system (especially some of the more powerful ones), but there are some with a longer duration that may as well just be permanent while grouped. It doesn't add to the fun, or take any skill, to recast a buff every 30 minutes or so. It's also easy enough to keep it under control, through having to be close enough to the caster to receive the buff, and needing to remain in the party.

So are there any good reasons that this shouldn't be a more common feature in MMOs? Is it something that you'd like to see more of in upcoming games? Tell us what you think.