I have a bunch of domains that all fall more or less in the same category niche, can I host them all on the same account without having any effect on rank?
Linking between the sites will be less strong than linking between other sites. if the sites are all on the same subject you should not link them!
google recognize same ip and will not entertain them accordingly. e.g if all your sites have a link to domain.com google will consider all those links from same ip as links from same website, even they are not
Many hosting providers allow you to have a unique IP address for each site, even they are hosted on the same virtual machine. This should help with the unique site issue described by salman4raza. I would check into getting unique IPs for each site.
Ok so you are saying it is NOT a good idea to have all sites on the same account? So I have to pay a hosting for each site....