Sometimes it's rather obvious, even without knowledge of IP addresses and the like. Medved, for example, has a habit of recycling the same material over and over again - which is what got him banned in the first place, actually - and so it's usually only a matter of time before something sets him off and he reposts something instantly familiar to people who know his usual style and material. Presumably the IP address is merely the final nail in the coffin, in that case ;)