I applied a few times over the past few months. The last time I submitted an app based on a big traffic jump on one of my main sites was at the beginning of Jan. I got an acceptance email on Friday morning, pretty good since Adsense was paying me approx one fifth of what I'm usually accustomed to making.
Might be they cut more people than they realized and needed to kill some inventory so they reopened acceptance in the program.
Now if I could only get phpadsnew (now Openads) working with maxmind to geo-target. Everytime I try it I get a blank spot where the creative is supposed to be. Don't want to get banned right after I am in.
I applied so long ago I've forgotten when it was. A year ago maybe? They finally called me on the phone and invited me to join a couple of weeks ago. I'd forgotten that I'd applied, but I'm giving it a chance. So far, not as good as AdSense. Targeting is poor, ad inventory doesn't seem very good and so my clicktough rate is low. Each click pays pretty well, but there aren't that many clicks.
If you have a good site with decent traffic, they'll probably get to you eventually. If you have a poor site or a site with low traffic, don't expect to hear from them anytime soon.