I haven't seen them used much in any of the open source Java projects I'm familiar with, I agree. We used them fairly extensively at my previous job, though, f

I haven't seen them used much in any of the open source Java projects I'm familiar with, I agree. We used them fairly extensively at my previous job, though, for implementing a mix-in pattern for boilerplate-free service endpoints, and they worked nicely. Outside of that, I use them al the time during development to add quick-and-dirty method call tracing when I'm trying to debug something. I personally think that they're very much underused, and having based an interview question on them for a while, not well-known at all.