I have a network of regional sites that do pretty well. There are about 5 or 6 of them and they are currently spread around 3 different servers.
The original reason was to give a bit of extra beef to the links with them being on different IP networks. However, now it'd be a lot easier if they were on the same or a pair of hosted servers I have for sharing data and being on the same platform etc.
Do you think it's still worth keeping them on different servers or can we assume Google et al know exactly who owns them and any benefit is mitigated?
As long as they aren't garbage sites don't worry about interlinking and hosting on the same IP. Any sort of penalty for this would be silly because it implies that a person cannot create more than 1 "good" website.
Also just be sure that these links don't make up a majority of your backlink profile.
Edit to add - I interlink sites on the same dedicated server.
[edited by: BradleyT at 5:22 pm (utc) on Mar. 26, 2009]