I think I basically just got sick of all the structure. Despite my hyperorganized tendencies and my deep love of lists, I was starting to feel extremely constrained by my normal reading routine. Every book I picked up had to fulfill at least one (and preferably several) of my challenges; I had to review everything I read; long books were out of the question because they'd take too long to complete. I pretty much stopped rereading books because they didn't count towards my challenges.
So I've decided not to drive myself crazy anymore. I'm still reading, but I'm not forcing myself to write reviews. I'm still participating in a few challenges, but they're much more manageable than the enormous 12 in 12. Most importantly, I'm actually reading whatever I want to read, without having to think about challenge requirements or boosting my reading total. I've even been rereading things, which has been glorious!
So anyway, that's why I haven't been posting or commenting very much lately. I do feel bad that I haven't been reading other people's blog entries, and I hope to catch up one of these days! I'm still around, and I will still post on occasion, but my online presence will likely be much more sporadic for a while. I hope that I'll eventually regain my motivation to be an active book blogger. In the meantime, though, I'm enjoying myself, and I definitely think this is the right decision for me right now. So happy reading, all, and I'll catch up with you later!