Some of these may be minor redirection sites being abused.
One operator of such a site contacted us bemoaning the abuse and also contemplating shutting it down due to it.
If only these URL redirectors checked the target URL in URIBL/SURBL the first time it gets submitted and also during the runtime, every time it gets accessed, it should reduce the problem immensely. I guess plain laziness to combat spam ain't going to work ;)
cheers, skar.