Sometimes, when the game is complicated. I read the WoW manual to get a quick grasp of the basics, and it helped me get started. The amount of questions asked by 'noobs' (I hate that word, but it's use is justified here) in trade channel which would easily be answered by reading the damned manual before you start playing is just....uncountably high, quite annoying.
I almost never read the manuals of sequels or pretty basic games (except for shits & giggles every now and then), like shooters. Even though Resistance 2 was my first PS3 games, I didn't touch it manual. Why would I? It's an FPS, can't be that hard, even on a console I never played on before. And whatya' now, it wás easy.