Forum Moderators: Robert Charlton & goodroi
One disadvantage you may have is if these domains link to each other. Google might see you as a spammer unless the domains are all very strong in their other backlinks from around the web.
In terms of "generic" blog hosting, all the majors are OK, I'd say. But if you're very serious, it's better to host your own installation so you have more flexibility to use any plug-ins that you may need, and to respond to different issues that can come up.
My sense is that if you have good reason for multiple domains, then simply be up front about it. Register the same whois information, and even share the same IP address when that makes technical sense. The more steps you take to hide the relationships, the worse it looks when it is discovered.
However, different domains should serve distinct purposes, and not be just a reordering of essentially the same information. If there is a distinct purpose served by each domain, and there is substantial unique content on each domain supporting those purposes, then all is well.