Generally, most affiliate programs (including Clickbank) have a tracking or analytics system set up. You can view how many times your affiliate link was clicked there.
If you are promoting an affiliate product in the Clickbank Marketplace, just log into your account. Click on the Reporting tab.
Then click on the Analytics tab.
Once here, go to the section titled "Affiliate Reporting." Set the "Report By" setting to Publishers. Set the date range to what you are interested in (the last week, the last 30 days, etc).
This will give you a list of Publishers (ie. the owners of the affiliate programs you are promoting) and a number of useful statistics like Clicks (Hops), Sales, etc.
You can easily see which affiliate programs are getting clicks and more importantly, which ones are getting sales.
And this is really key. You will find that some of the affiliate programs are duds (meaning that the sales conversion ratio is very low). I just had to stop promoting a program because it had 402 hops without a sale.
But that's fine. Now I know, and I can start sending the traffic generated by articles for it to a different affiliate program.
And you will also see your winners, and can start putting more energy into promoting them. I have one affiliate program that results in a sale for every 47 people I send to the salespage. I have just increased my efforts with it because I know that its profitable.
Hope that helps.
JoeMack