Note that the NTL problem has been solved (presumably through some horribly ugly special cases in the MediaWiki code) - now, NTL users should see their real IP, the one they see with ipconfig or ifconfig. Could some NTL users please test this?
It seems to work perfectly for my NTL home broadband connection.
For the NTL corporate connection we have at work, it came up with an IP address I can't ping or traceroute, but still one that belongs to NTL and isn't a proxy. That IP address had several earlier contributions, going back to December 2004 (my company moved to this building in November 2004), so blocking it would perhaps create potential for collateral damage by excluding the whole company.
Timwi