There's been debate about an old essay at the Alexandrian, which has recently been updated. The original injected the catch-phrase "dissociated mechanics" into our community's arguments, and like other buzz-words (like "fantasy heartbreaker" and "game balance",) there are so many interpretations of what the phrase means that it's become practically meaningless, more like signal to start fightin'. Jeff Rients has raised a few objections to points made in the essay. I have my own objections, which I feel Jeff approaches but doesn't quite focus on in the same way I would.
The way I would define dissociated mechanics -- and the point of contention about them -- is: mechanics that make you engage with the rules instead of the fiction. The problem with some mechanics is not that they don't have an in-game explanation for what's going on, or that the explanation comes after the fact; it's that the activity at the table switches from what's going on in the fictional world to who's going to win this little mini-game.
(This, of course, ties into my own peculiar definition of role-playing games, but I think people can grasp my objection without getting into that side-topic.)
In the Alexandrian essay, there's an example of a One-Handed Catch ability: once per game, a character with this ability can make an amazing one-handed catch. I think it's a poor example of a dissociated mechanic, even using the definition given at the Alexandrian, because people have analogous experiences in real life all the time. How many times have you witnessed someone do something amazing, and afterwards the person says, "Man, I wouldn't be able to do that again even if I tried!" There's nothing really dissociated about the One-Handed Catch ability as described.
Now, imagine instead that the ability, instead of being "once per game", is "once per action point spent". And you earn action points by reciting catch-phrases at appropriate times in the game, with the appropriateness being determined by popular vote among the other players. Or maybe action points are linked to a bidding/gambling mechanic. In either of these cases, you stop talking about the fiction (catching something with one hand) and start engaging with/becoming interested in the outcome of a non-fictional activity.
Those are dissociated mechanics, in my opinion.
Some people like that kind of thing. For them, the fiction is important, but not as important as the back-and-forth, game-like aspect, the gambling, the bidding, the deep knowledge of the rules or the masterful planning. Other people prefer the fiction, and the less of the other stuff going on, the better. This is what is being debated. Some people don't like deeply tactical, game-y mechanics, no matter how many times other people tell them "but that's what's fun".
It's like the idea of "simulating" fear or tension in an RPG using Jenga mechanics. Some people like Jenga and especially like the idea of tying fictional outcomes to Jenga. Me, I don't care for Jenga or games like that, so why would I want to stop playing an RPG in the middle of an interesting bit, just to play Jenga (or poker, or any other game?) Telling me "but it's more fun that way" doesn't convince me; if I thought Jenga was fun, I'd play it instead of D&D. The fact that someone else really enjoys something doesn't make me enjoy it, too. And the fact we're interrupting something I do enjoy to do something else entirely doesn't do much for the game.