How long has it been since your friends bought the ads?
You may also have to approve the ads before the ads will be shown.
I have used adbrite quite a bit and haven't had too much of a problem with them. I usually use them for getting traffic to my sites though. They have some advantages and dissadvantages compared to Google or yahoo.
This is a great question you are asking because Vladimir and I will be releasing a new advertising product soon that will enable you to make ALL the money from your ads!! That's right. 100% would go to you. As you know Adbrite, google, yahoo, text-link-ads all charge you for the ads on your site.
Why pay adbrite any of the money for the ads that YOUR friends are buying?
They didn't do anything to find you the customers.
Our product should be ready in a matter of weeks, if not less. Stay tuned.
Tim
ps..You can call adbrite. I have before and they were helpful. Try the support and find out what is going on.