I'd love to be able to think of a side project I'm actually enthused to work on. I don't know if I'm burning out but nothing really seems interesting enough to me to put the effort in.
At this point I don't feel guilty anymore when I'm not feeling motivated, because I know it'll be back some time soon. At the beginning I'd get worried I'd never be motivated again, now I just treat it as a "part-time vacation". Read history books, play tennis, cycle and enjoy my family. :)