First off, I'm not one of those people who collects lint or something strange like that, and the mug is sitting beside the pile for size comparison.
While doing my laundry the other day, I was cleaning the lint screen on my dryer before each load like I always do, and I got to thinking that it had been quite a while since I'd cleaned further down into the dryer vent. So I went to it and that's what came out. Here's a link to show you exactly what I mean (just so happens this is exactly what my dryer looks like too).
As gross as this is, it is also scary... scary in the sense that this could have been a fire waiting to happen. You always think it could never happen to you. Needless to say, I'll be doing this extra step from now on on a regular basis.
Have you cleaned your dryer vent lately?