My parents got really pissed when I ran up a $250+ bill on CompuServe, dialing in on my C-64's MiteyMo 300 baud modem.

Now that was an experience - most people can type faster than 300 baud!

There was a joke soft called 'sl' circulating among Japanese universities (I don't know if it went out abroad). It just showed an ascii art animation of a steam locomotive running across the screen. It was irritating, though, when you mistyped while logged in a Unix machine via a 1200baud modem...

sl is still around, and at a minimum easily installable on Ubuntu (apt-get install sl)