No matter what I do, whether I choose daily, monthly, or yearly sales the graph stays at 0.

This might be an undocumented fault with their site?

LOL.  Mine works.  It shows a humongous skyscraper like bar from early July when I had my 1 sale.  Be patient.  They promised an ad campaign this Autumn.  We will hold them to it.

lol ...

hey. so jealous. you got sale/s

5 sales on 1 aug.. probably from one buyer.. but still nice to get 5 sales, and the fact that they sell in euro is also nice.

oh yeah, and i forgot this   
http://yaymicro.com/register.action?referredBy=leaf

I had my first Euro at Yay, and on the 1st of August at that! So my graph starts looking right

Oh and here is mine: http://yaymicro.com/register.action?referredBy=Nemo1024

0 sales in last 50 days....

I will probably close my account by the end of the year at YAY.

Well, I had 2 sales in the whole July at iStock (and 4 in June), but that is no reason to close my account there. I would advise to wait and see until Yay had time to spread its wings.
On the other hand, if you quit your account, I will get less competition...