TombombadillyTV
I've Got It
I don't think there's a definite number, I just randomly got them a few days ago about an hour after I realized how cool it could be if I had them 
I'll have 15,000 total video views soon and I have 9 videos. I think it depends on what your average views per video are. For example if you have 100 000 total views, but only because you have 1000 videos and your average views per video are 100 I don't think you would get them.[DOUBLEPOST=1349998254,1349998187][/DOUBLEPOST]
I had one of my videos taken down and so my account was not in good standing but one day it magically went back to good standing after a few months, so maybe yours will too?

I'll have 15,000 total video views soon and I have 9 videos. I think it depends on what your average views per video are. For example if you have 100 000 total views, but only because you have 1000 videos and your average views per video are 100 I don't think you would get them.[DOUBLEPOST=1349998254,1349998187][/DOUBLEPOST]
Reading through the comments I came to the conclusion that you have to be active on Youtube and your channel must be in good standing. Which makes me wanna ask a question - due to a stupid mistake I made I got one strike against my channel (because copyright violation), so out of the 3 points I can see on my channel's settings page 1 is red (because of this warning). Does that mean that I won't be able to use custom thumbnails?
I had one of my videos taken down and so my account was not in good standing but one day it magically went back to good standing after a few months, so maybe yours will too?