It isn't the most fun in the world, but it's fairly profitable. Owning rentals is part of our retirement plan, and I'm stating the obvious here, it's so much easier when you have good renters. I've met with potential renters, and told them "No" after speaking with them, especially if they have pets. If possible, I try to wait for the right renter, but sometimes it's nice to have a warm body in the unit to collect rent from, instead of letting it sit for too long.
And renters can be a$$h@!es, especially the squatters. I don't play very nice when you're trying to use the law to live rent-free in one of my properties.