r there anything bad about hosting adult sites? do they cause a lot of spam? what things can cause a lot of load on the cpu? And should I make everything unlimited? ie. unlimited mysql databases, unlimited subdomains, unlimited aliases?

As discussed here before, hosting adult sites would need several additional levels of enforcement either by the web host and or server administrator, things such as ensuring that the materials hosted are of legal nature (web host has the legitimate copyrights to the materials and that the items listed are legal by law) and that only the appropriate people (age group) have access to the sites.

I am not sure if this is of any baring but I do tend to get more spam based on an adult nature than those which are of a general nature.

As for Sever Load, running of scripts is the one which creates the bulk of CPU load, this includes database access, email access, streaming media and so on. If it is just pure text based HTML or pure file downloads then there may not be as much strain on the server.

No, it is best not to set everything as unlimited. Only set the limits to what you can honestly deliver. If you cannot deliver unlimited then do not do so. This will also prevent any legal complications and also abuse by the clients.

We publish and host adult sites. I believe we get more SPAM regarding prescriptions, penile enlargements, and HGH than porn/adult sites. However I agree that allowing unlimited sub domains, and databases will directly affect the server load. Unlimited aliases, POP3 accounts are fine as they are only unlimited within the scope of the customers allotted diskspace.