Personally, I see the point in it, but I take things a step further. Rather than banning single IP's, I ban entire IP ranges (but only if someone in that IP block "grows a brain" and tries to do anything "fishy" to my systems).
So far, I've blocked mainly the APNIC ranges, as this seems to be a big source of the "fishy" activity. But, I've also banned some ARIN and RIPE ranges too, with just a tiny handful of LATNIC ranges tossed in the mix.
Keeps the idiots from having a second shot at me, and keeps me "safe as can be," considering no firewall is absolutely 100% fool-proof and hack/exploit-proof.
With Dynamic IP addressing used in some DSL, and almost every dial-up service, it's too easy for some idiot to get a new IP and try again. So, I just ban their ISP's IP ranges. Screw banning single IP's, lemme cut myself off from the world, one ISP at a time.