Last night I sent my first ever facebook invite to all of the suggested list that facebook had for me. I also pulled any contacts out of my google account that have accounts and my AIM account. Unfortunately, I forgot to keep track of exactly how many were sent and facebook doesn't provide that information. Probably so you don't see the count at a later date and realize that 78% of people you invite ignore you. Luckily I do receive an email when someone accepts which means I have SOME data.
Through the magic of array formulas, google spreadsheets, html, and too much time on my hands - the above graph will keep up to date when I add data.