I tell you what we did (which seems to be working): 1) Launch your free product (the free part of the freemium). 2) By the time you get it tuned up, you'll hav

I tell you what we did (which seems to be working): 1) Launch your free product (the free part of the freemium). 2) By the time you get it tuned up, you'll have a strong sense of where the pain is (and hopefully a reasonable guess of where to put the pay wall). 3) Put up a little permission marketing form that essentially says, "Hey-- we're going to launch a premium product soon that does this, this, and this. If you want to hear about the launch, give us your email address". Measure how many of your free customers sign up for that. 4) Look at the resultant list for interesting email addresses and send a personal email to some of them asking them if they'd want to dive in as pilot customers and help shape the product. #3 helps you confirm your understanding of the value of your premium offering. #4 gets you your first customer. If you don't have the sales-fu to reach out to pilot customer candidates, just launch it quietly, email a subset of the list who signed up to hear about it, and measure signup percentage (which will be WAY lower than you think it will be).