For Windows Vista Logo, we used to have vouchers to entice early adaption. An ISV recently asked me for vouchers for Windows 7. Since Windows 7 is a "self-test" there is no need for a voucher. It is virtually free. The only cost might be that an ISV needs to buy a certificate to log in to winqual (which is where you would submit your test results).

https://connect.microsoft.com/site/sitehome.aspx?SiteID=831