I've seen sites listed on FM that have far less than 1M uniques. Given that we get thousands of uniques a day, it seems like we've graduated from Adsense, but not enough for FM? Dilemma...
I tried FM (my site has 800k-1.2m page impressions / month; mainly US traffic) and they said 'come back when you get 1m US uniques. But you're right - they have sites that are definitely smaller.
Where does your traffic come from? How many page impressions per user?
Also worth keeping in mind that FM takes a 50% cut.