Magic Find, as implemented, is a bad mechanic, and is counter-productive to co-operative gameplay.
If I run a dungeon in full MF gear, along with food, I can reach somewhere in the area of +165% Magic Find. This results in a vast and basically immediate increase in the quality of drops that I carry away from the dungeon. This benefits only me, as drops are not shared.
However, the difference between running full MF gear, and running gear with stats that are meant to make me more effective is just as clear of a difference. When I run MF gear, I have approximately 20% less max HP than I do with my good gear, and I take approximately 33% more damage. The damage that I deal is lowered by a similar amount, and the healing that I can provide to myself and the group is cut by nearly a third. My food ‘slot’ is also taken up by MF food, leaving me unable to use another consumable which might make me more powerful, give me more regeneration, or have some other interesting effect.
I am effectively only half of a party member when I spec for Magic Find. My entire party will feel the difference, and the burden of having to make up for my reduced stats must then be shouldered by the players who I am ostensibly supposed to be helping.
I don’t personally like the idea of Magic Find, period, but it’s not such an evil mechanic that I think it needs to be done away with completely. Giving the player the choice to effectively ‘downlevel’ in effectiveness in tradeoff for getting more/better loot is a legitimate gameplay mechanic.
However, in its current implementation, the benefits of Magic Find are realized only by the player actually using the stat. And the penalties associated with Magic Find – significantly reduced character efficacy – are spread out and shouldered by the entire party.
In other words,Players are being incentivized to harm their own party in exchange for personal gain. The ideal situation, from the perspective of an individual player out for purely personal gain, is to be in a situation where you are the only person in a party with Magic Find – You receive the full benefit of stacking your own Magic Find, and the rest of your party is best equipped to pick up the slack.
In a game like Guild Wars 2, which has gone out of its way to reinforce player-friendly behaviour by eliminating concepts like fighting over (universal) loot or ‘kill-stealing’, I have difficulty believing that this is the message that ArenaNet intended to send their players.
The best solution, in my opinion, would be to add up and average the entire party’s Magic Find bonuses. This wouldn’t really do anything to stop a player from reducing the party’s overall effectiveness with Magic Find gear, but it would allow the entire party to share in the benefit that is intended to balance out the reduced effectiveness.
It’s hard to tell whether this problem is particularly widespread, or how serious of a problem that it is, because a player really has no easy way of telling at a glance that one of her party members is holding the group back. Regardless, I think it is at least potentially a significant problem, and I think that fixing the imbalance sooner rather than later could prevent this from becoming a serious issue for players.