WoW's new random cross-server LFG feature has so many caveats and exploits with it that it made for one of the longest walls of blue text I've ever seen in a single post on MMO-Champion. The one that interests me from an incentive design perspective is the use of the deserter debuff.
The idea is that players will be locked out of the system for 15 minutes in the hopes of discouraging them from fishing for better groups/dungeons. This kind of sort of works in battlegrounds because battlegrounds are intended to be run repeatedly. Deserting a match because you don't like how things are looking means spending 15 minutes that you were planning to spend on PVP waiting out a debuff.
By contrast, many players will do the new random daily 5-man feature precisely once per day, because you can only earn top-tier raid emblems once. A good group can clear many heroics in under 30 minutes, but there's no upper limit to how long a struggling group may take.
If you're only in it for the emblems - and the emblems alone brought many people back to 5-mans in patch 3.2 - you weren't planning to do another dungeon run after this one anyway. That reduces the effective cost of deserting, because you can just do your daily quests, auction run, etc while you wait for the timer instead of after the dungeon run ends.
Bear in mind that patch 3.3 will have 16 possible random 5-mans dungeons. Of those, four offer loot that's 1-3 tiers above the rest (the 5-man Icecrown dungeons should be approximately on par with anything up to 25-man TOC), and another handful are quick and easy for even the weakest group (e.g. HVH, HUK). If you don't get a good dungeon, or it looks like you group can't hack it, the incentives say that you should quit and try again. No amount of restrictions and exceptions that Blizzard adds to the system will stop players from doing just that.