haze said:
Have you considered consulting with a fortune teller ? :D
I was going to say keep creating them until your server seems slow and then delete one, but I think I like yours better. :D
If you are the server admin, then the only limit will be imposed by the performance hit on your box. It is impossible for me to say how many sites will fit into your accept performance window.
If you are a reseller, then you will have to ask your host.