IP address to physical location mapping

On every web site where I can configure the web server parameters (sadly not available in all hosting environments), I catch the ASP errors (500;100 error page), acknowledge them to the web user and report them in an e-mail to the webmaster (if you can't debug every possible code path, it makes sense to fix the bugs once the first visitor hits them).

Sometimes I would also like to figure out where the visitor causing the ASP error is coming from (more so if the errors are due to lack of resources, indicating unexpectedly high load). The usual tools (nslookup) fail if the ISPs don't enter their IP address space in reverse DNS lookup zones. In the past I've tried to use various Internet registries to figure out who the address is allocated to … and finally I've stumbled on the IP2Location web site, which does exactly what I was looking for: I enter the IP address and it tells me where the visitor is coming from (including a nice overview map for those who have no clue about geography).