This is funny. I worked for dyndns over the summer and keeping this up is one of their major concerns. I think it runs on several different servers around the world, anycasted. Tons of router manufacturers from around the world put something like the above snippet with checkip in their code, as well as people like you and me who use this as a quick hack.
Or you could use http://geoip.ubuntu.com/lookup which the Ubuntu installer uses for default settings. It's all returned in xml and gives current location and timezone as well as IP address (not that I've ever woken up with no idea where I am of course)
I run my own version, with a fair bit less 'frill'
curl -s http://www.lusion.co.za/ip
No ads, no style, no frill. Returns one line of machine readable text. Get you IP right on the command line with curl: