Sugar will definitely burn, especially white sugar. I use turbinado a lot, as it seems to not burn as quickly. My thoughts are probably more along the lines of what "Fire it up" is asking/saying about the wood just due to your smoke comment.
May have just been over cooked too, that is possible. I cook mine by sight more than anything. A quick way to tell is to pick up a slab by say the third bone in, and if it bends at a 45 degree angle and starts to tear away, then they are done in my book...they also just have that look about them which I can't quite describe. Take a look at the 3-2-1 method (oops used to be a how-to document here). Generally 3-2-1 for spares and more like 2-1.5-.5 for me on BB's depending upon how loaded up my cooker is. Not trying to tell you how to cook, just trying to help because I don't think we have your problem figured out yet.