I think theres been a few points missed out on this topic!!
Ad supported free hosting is all fine & dandy until your ad publisher gives you the foot up the backside and terminates your account.
illegal click throughs will happen theres no doupt about that, The user may simply think he/she is helping you out or visa versa wants to get rid of the ads on their sites...
You gotta think things through first if your planning ad supported..
Bidvertiser is not an option for ad supported as they check domains plus you have to ad each domain, sub-domain is usually not a problem.
Google Adsense have very strict TOS, They booted me.. :confused4
Post 2 Host
As some-one mentioned earlier in this thread, you have the chance to check who you are gonna host in a post to host enviroment.
And its a better way of poaching them of their free hosting onto paid hosting, Most ad supported host never get the people they host on their sites unless something goes wrong.
More importantly your not gonna make money from free hosting, 80% of the time you wont cover the cost of the server.
You do it because you want to!!!