Well there are rumours that if you want to build a High PR Blog network you should build them on different Class C IPs instead of different Class D IPs in the same network.
So people say you should build your sites on:
212.112.203.156
212.112.94.194
212.112.85.123
Instead of
212.112.203.159
212.112.203.94
212.112.203.75
Atleast thats what most SEO "Gurus" say, and I've talked with a few people that high PR networks and they say it looks more natural if your High PR links don't come from the same class C, becouse if they are on the same class C it usually means that they are hosted on the same Host/Server so its easier for Google to determine you are trying to manipulate the search engine results and that Google might not count all of your Links or give them less weight.