http://www.seobook.com/
Or just one?
Let’s take look at a web strategy that has a number of SEO and benefits: the hub and spoke strategy. A hub and spoke strategy is when you create one authoritative domain (the hub), and then hang various related websites off that domain (the spokes).
If you don’t yet have an authority site, it’s probably best to focus on that one site. However, once you’ve built an authority hub, it can be a good idea to specialize in a number of niches using multiple, smaller sites.
Let’s look at a few reasons why, in the context of dominating a niche.
Economics
Economic theory holds that division of labor increases profitability.
During the early days of the web, it was easy to make money by being a generalist. However, as the web got deeper and richer, it became difficult to maintain a generalist position unless you had significant resources.
Specialization, by way of niches, allows for greater targeting, and this targeting can increase value. Leads and advertising become more valuable, because the target audience can be reached more efficiently.
The hub and spoke approach is this theory in microcosm. The hub is the generalist authority, whilst the spokes allow for niche specialization.
We’ll see how this dove-tails with SEO shortly.
Full article: http://www.seobook.com/should-you-have-multiple-websites
article suggested by Ondrej Ilincev