I had been using idevaffiliate since last fall, and while it is good, it is somewhat limited for some things.
I was directed to a new piece of software (script) last week and I have to say, at first I was skeptical (since it was so new), but after installing and testing, I have made a complete switch over from idev.
Their marketing plan is genius. You can download it for free and then once you reach 250 affiliates, you have to buy the license (or don't use it any longer). This free version is a fully-functioning version, too, with nothing left out.
There are lots of integration options, including Amember, Zen cart and a whole host of other modules.
You are not limited to 2 tiers, affiliates can email their downline affiliates, you can do affiliate refunds (not available in idev) and a lot of features that idev does not have.
Support is second to none. There is a support forum in which you will get answers to questions and issues right away, no need to submit support tickets. There are live bodies right there waiting to help.
I have it installed and integrated it with both Zen cart and Amember. We just finished all testing today and it works beautifully to really create a nice automated system, leaving me much more time to concentrate on growing my business.
It's really worth checking out.
http://www.commuteinyourjammies.com/jroxjam.htm
Patty