At certain point of your blog's life journey - as your blog increases in popularity - there will be times that some smart advertisers approach you to place geo-targeted ads on your blog, must probably due to your blog ranking so well on certain region and get considerable blog traffic from that region. Chances are, for such needs, your advertiser will pay you a premium - so, you can't simply give up on such request, I suppose?

So, they will need to give you advertising details along with cookie to detect the geo-location of your originating traffic. Now, as a blog owner, you'd typically wanted to work things around for your advertisers.

Here are probably your typical questions: How to be able to serve geo-targeted ads and check whether the ads are displayed correctly to the targeted region?
Displaying geo-targeted ads

If your blog runs on WordPress, there are some WP plugins that can help you place geo-targeted ads on your site - just search for "geotargeting" on WordPress plugin directory... the "Who sees Ads" free WP plugin and MaGiKS Geo Country Lite might also do the trick.
Checking geo-targeted ads

The next issue - how do you know that your ads are really displayed in the targeted region?

To check geo targeted ads, I recommend you to try GeoSurf.

GeoSurf allows you to surf by location. So, you can see what local surfers see without even the need to actually live in that region.

So, for example - if you want to display ads relevant to UK audience, you might want to use GeoSurf to do proxy surfing, allowing you to see the ads on your blog as if you were living in the UK.

With GeoSurf you can actually choose from more than 80 global locations.
Some other purposes...

Not only to check on your advertiser's geo-targeted ads, GeoSurf can help you to see what your blog's AdSense ads displayed on particular region; you can also access websites that block your originating IP address to see what they are up to; you can also check on your competitors; and many more usages.