The comment to one of my previous posts reminded me of a cool feature that's been available in Cisco IOS for a number of years - you can change how the IP addresses and routes are displayed in various show printouts (but not in the router configuration) with the terminal ip netmask-format bit-count|decimal exec-level command. You can even make the change permanent by configuring ip netmask-format format on console and VTY lines.

And the funniest part of the whole story is that I was utterly impressed with the feature when it was introduced ... and now almost started to reinvent the wheel and implement the same functionality in Tcl