Wordpress blog, need advice on keywords

Hey,

Basically I have a site that's a technology related Q+A site. I answer questions that I find in places like Yahoo Answers, Amazon Askville, etc.., along with doing some reviews and such. I have 11 different categories in all.

My question - should my keyword efforts treat each category as it's own "niche", or should I focus more on the keywording of the site overall? Hopefully that makes sense

Thanks,
J