I am using blogger blogging services . Don't know how that one works but hope that it is not unique for everyone .
I use them on all sites that I am truly trying to get organic ranking. I can't say that it is a major benefit, but as we all know the small seo bonuses add up after a while.
I have several IP addresses on my dedicated server. Reason for it is: Grouped regular sites under one IP Groupd experimental/controversial sites under another IP Also for one site I needed to track the subdomains, which I create for new users, which are using the site. So I use one IP for that site alone, cause that made it easier for me to set it up and to route all of them with a wildcard to the same IP.
I know that your suppose to rank better if you have your own ip address but how many here with their own ip address can confirm this.
The biggest problem with sharing with other sites is that web sites load very slow. On the other hand you can't beat the price.