Trackers` problems

You know that trackers are not perfect . What do you think is the main problem that can be a potential danger of private torrent trackers ?
(for example lack of donations , security, banning by The Scene, ratio cheaters, invite trading , hacking , MPAA & RIAA , ISP`s restrictions and throttling etc.)

i don't think that is good to talk about trackers problems , because some people may learn how to exploit those ''bug's'' and the tracker is down.