Quite a few of my students have their own web-sites that are often promoted in their e-mail .sigs. I always make an effort to check them out as I usually learn all sorts of interesting things. For instance, what hairstyles they don't like, who the most boring lecturers are, what types of consultancy they offer ;-), etc., etc.

Call me evil, but I like replying to their e-mails with a wee snippet gleaned from their site. For example:

the lectures so far have been so boring that i've starting drawing cartoons on my lecture notes.

Surely not in my lectures ;-)