In my experience, around 75-90% of your submitted memes will get featured (appear in "latest")
I've also noticed that memes using non-standard templates, gifs, and demotivationals take longer to get featured, probably due to them being reviewed by the moderators. Memes with non-standard templates are also less likely to be featured at all.
If by featured you mean appear on the front page (first page of "hot"), only a small percentage of them will get there.