I'd love to see an ability to send an email to an affiliate when they reach a new tier.
Example: When an affiliate reaches gold status, they receive an email something like this:
"Congratulations, you're now a Gold Affiliate. Way to go. You're now earning 15% commissions on all sales you refer.
Oh, and here's a one time use coupon code for you. Receive one free Hammer Slingshot (fill in with your product) with coupon code GOLDAFFILIATE!
Claim that free slingshot and use it to drive your commissions even higher!"