I am behind on a bunch of different series that I follow. As I mentioned yesterday, I am 3 collections behind on Jack of Fables (though I did go out and pick up the 3rd volume, thanks to a coupon and some more of that tutoring money). I started reading Scalped earlier this year and loved it but I'm 2 volumes behind with a 3rd out soon. There are now 6 100 Bullets trades that I haven't bought, a series I really want to finish. And that's just a few Vertigo titles off the top of my head.
Don't get me started on the big ticket items like Starman Omnibus (still need the 3rd volume), Nexus Archives (only have 2 out of a soon-to-be 10), Asterios Polyp, and Darwyn Cooke's Parker graphic novel.
I've actually made the decision to revert back to trades a couple times this summer but just never followed through. This time, I have to. And I will.