I read the article A Night With the World's Most Hated Bands by Chuck Klosterman. Pretty good article. A little snobby, but he does well considering he's a rock critic.
Klosterman says there's five bands it's "okay" to hate for no reason: Bush, Hootie and the Blowfish, Limp Bizkit, Creed, and Nickelback. He saw the last two of them play live the same night and dissected the reasons people hate them. He boils down the Creed hate to people thinking they were Pearl Jam ripoffs. He says Nickelback's hate is just because; there's no reason.
My take on the Nickelback hate: They're the most popular of a lot of similar bands. A lot of these bands are worse than Nickelback. Hinder, for one. Also Puddle of Mudd. Some of these bands are better - such as Shinedown. When people say they hate Nickelback, they mean "I hate post-grunge music". I don't like Nickelback, and I don't even care for Shinedown apart from a few songs. But I like Foo Fighters and Switchfoot. Before I got into Muse I thought they were another post-grunge band and now they're one of my favorites. I can't dismiss the whole genre.
I don't like Nickelback, but some of my friends do. I also don't like the Velvet Underground or the Pixies and some of my friends do. I'll leave any room where the Verve's "Bittersweet Symphony" is playing, but some of my friends like it. I don't know why, because it sucks and I hate it. But people have different tastes. I won't judge somebody based on that.
I also like a lot of music the critics hate. I like a lot of prog rock, which many music nuts dismiss with the wave of a hand. However, prog rock gets a lot more respect than Nickelback or Creed on sites like Rate Your Music.