I pronounce it \oh-tah-koo\. In the past, it wasn't a compliment to be labeled an \oh-tah-koo\, though one of my Japanese friends says this has changed a little since Westerners use the term in a playful way without its negative connotations. It's not a term normally bandied about unless you're associated with anime and manga.

Can you hear the reporter say オタク here at 0:02 http://www.youtube.com/watch?v=yD16LsrZJuQ

English speaking people is the "ou-ta-kuu" is that it tend to pronounce. "O-ta-ku" correctly. Please try and pronounce "O", "Ta", "Ku" Do not pronounce the "U" part of "O". I think "ta" is okay as it is. Please try not extend to pronounce the "U" part of the "Ku".