It is important to place the code as described here to make the advertisement non-contextual if you are running Adsense on the same page.
I can’t say I will get to the same levels as Darren, but I am joining new affiliate programs all the time. If I can get a few sales in the first few weeks, I keep with the program. If I don’t get a single sale after a few weeks, I dump the program all together.
It is great to go to your mailbox and actually find money in it rather than the usual bills.