I've set up about 30 arbi sites now and each one has it's own subdomain of one domain. Do you guys think I should start using another domain or just keep rolling with it?
Keep letting it roll Jdog. The only concerns you have about subdomains and mass building are related to if the main domain gets banned from the indexes. With an Arbi you are not dependant on SE indexing to bring you traffic.
For Arbi sites there is no difference. The directories are easier to manage but with subdomains you have more possibilities if you want to make subniche (directory) in your niche (subdomain).
Thanks for the help guys. I just looked at how many subdomains I had and it looked funny and I didn't want to have my host get pissed at me or anything.