I spent most of the day trying to figure out how to modify our error handler class so that multiple threads could write to the same log file. (This is not improved by the fact that our "log file" is actually a bunch of string arrays in memory for most of its life.) After playing with various designs for the stacked error handlers (which install on top of one another on a per-thread basis), I finally realized that the easiest thing to do was to dump the contents of each thread's log back to the parent thread's log when the thread terminates.
Of course, this meant all of the code I'd been playing with was completely useless. But Doug and I did get to explain the concept to the programmer who's going to implement it.
Now, I'm back to the Debt Scheduler, where I've fixed another parser problem in the new functions that I added. I'd ask "Why doesn't anyone test these things?", except that no one has started testing this bit of functionality yet and I'm still unit testing as I clean up around the edges of the feature.