It is interesting to note that the Cish Perl programmer is the one who suggested the training day and largely because he was very impressed with the way I managed to tidy some of the Cish code he'd written and wasn't happy with.

Sure you can write any old crap that works most of the time in pretty much any old language, but by knowing a little more of what's possible with whatever tool you are using you are likely to get better use out of the tool. The purpose of the training day is to show some of what's possible. The reason for asking here is to get a broarder idea of the things people think important so I can make a better informed decision about what to include and to what depth.