d3vrandom - 7:49 pm on Oct 11, 2011 (gmt 0)

Well you don't have to share the host. I mean you could have all the sites consult a central database server. It would be slow but no different from your current proposed system. Another option is a memcache server to speed things up.

But I am curious as to why do you want to do things this way? I mean why not just use different IPs for the different sites and host them on the same server? If SEO is a factor you can get IPs in different subnets at certain providers that cater to this sort of demand.