Most of my online income is from the IM/MMO niche, and a few other niches that are filled with buyers looking to solve problems. Its easy to make money in those areas, because people are actively looking for solutions.
I know that funny cat videos and the like can draw a lot of traffic and benefit from a lot of social sharing, but it doesn't seem like it would be buyer traffic.
There is certainly a market for cat training guides, cat health information, cat toys/accessories, but I don't think focusing on those would draw the same volume of traffic as something like funny cat videos and I don't think the majority of people interested in funny cat videos etc are actively interested in purchasing cat-related products.
What would you do with a great cat related domain if you we're seeking to monetize it?