Blocked Referers

I finally got annoyed enough by people abusing my referer list that I have spent an hour this morning writing a filter process. I haven't formulated a policy as yet but if a referer is dodgy (i.e. porn) or seems to be using my list for advertising purposes or to try and build their google rank then they will be blocked. Apologies to anyone this causes problems to but this is almost as annoying to me as spam.