One of the things I like best about the TCP/IP from a technical standpoint is that almost all of it happens in ASCII. This means that when your mail is getting refused or your web site isn’t working you can just fire up telnet, hit the right port and start poking around.
Alarmingly often I find that I can confirm and sometimes diagnose a problem with my ISP’s mailserver before they can. I also find it terribly handy for sorting out wonky behavior on my web server, though I just use an O’Reilly book for that (HTTP Pocket Reference).
I think it would be pretty useful if everything could be in Unicode, from OSes to networking protocols, but that seems rather a long way off. Just the ability to hack in telnet in your own language would be pretty neat. As it is, you’ve got to do things by rote or learn English. I’m glad I don’t have to do that again.