You can display statistics for your ads and spots. In each case the statistics show:
Impressions - the number of times that the ad was displayed.
Click-throughs - the number of times that it was clicked on.
This shows an icon for each site that the ad is currently being displayed on.
The statistics page will be displayed:
If you have multiple ads being displayed on a spot, the Impressions figure should be almost identical for all the ads, but the click-throughs will depend on the popularity of each ad.