I believe the way to find that is click the Cache on a result...and the IP will be there in the URL -- However I'm not 100% sure.
There are several FireFox extensions that provide a more reliable way of telling which IP address you are hitting. You can get one of them at http://blogs.jobdig.com/developer/2006/06/16/ip-extension-for-firefox/ .
Considering it's load balanced and such, what you get now is not a guarantee of what you'll get tomorrow, or what your neighbour will get etc.
Tops30, Yes, that is what concerns me. The results I am getting are pretty good for my keyword. However, when I run the mcdar.net/dance test I get completely different results, which are not good for my site and keyword. The DC I am getting is 72.14.209.104 My concern is my DC shows a pretty good result for my keyword yet I am page 2 on all the other DCs. Here I think I'm doing pretty good but maybe everyone else is seeing another DC?
Don't worry about it. Worry about 'generally improving rankings' without knowing exactly what ranks where for who. And worry about converting the traffic you DO get, don't worry about the traffic you might have missed because of datacentre flux.