If the discussion of Harvard political theorist Nancy Rosenblum's On the Side of Angels: An Appreciation of Parties and Partisanship at Jacob Levy's digs isn't enough for you, try this month's Cato Unbound, where Rosenblum makes her case for partisanship in today's lead essay. In the coming week and a half, we'll have replies from Cato's own Brink Lindsey, GW political scientist Henry Farrell, and Stanford's James Fishkin.
My problem with partisanship in the U.S. is that, due to the structure of the electoral system, there's really no place for more than two parties. My own disenchantment with active political participation is in part driven by the fact that there is next to no chance that any party I would be willing to join could be a real force in government. I suspect that in the possible world where the U.S. suddenly became a proportional parliamentary system, a party with roughly my politics could pick up a fair number of seats and would have a chance of sharing power in coalition governments. But in the actual world, the best I can do is be a Libertarian and totally irrelevant, or I can join the Democrats or the Republicans and be actively hated, for one reason or other, by my co-partisans. So, no thanks. 
I'm curious to see how my partisan sympathies shake out when I suddenly become Canadian.