Kill Ten Rats discusses with an intersting thesis -- we don't mind a grind so much as we mind one we can't advance without breaks.
Using the Guild Wars Wintersday redux as an example, the point is made that the holiday events are a straight-up grind -- but they're a constant one that you can pick up and start with no downtime, then stop whenever you want. Lord of the Rings Online and World of Warcraft have both taken the same approach with Skirmishes and the Dungeon Finder, taking the slow march to being ready for an instance out of the equation.
It's an interesting idea, that what we really dislike aren't the grinds but being stuck unable to make much progress in them. If you tend to think that grinds are the worst thing in MMOs today, it might be an opportunity to re-examine that stance.