Don't go overboard and have each blog on it's own ip or anything, but then again you don't want to cram 100 blogs on an ip. IP is one of many factors the SE's use to determine a relationship between your own sites, and if you are interlinking a lot then you may want to spread your network out over a few IP's or even better a few hosts. I generally do 10 sites max to an ip address depending on the size of the sites.
This article is actually pretty close to the mark, and touches on similar topics. Worth a read :
http://www.seomoz.org/blog/17-ways-s...alue-of-a-link