I've always been blessed with static IP addresses, which means that my mail server, Web server and whatnot always stay on the same address. Likewise one of my clients - their office has a pair of ADSLs, each with its own static IP range so that remote systems are able to make incoming connections.
Now, one of these ADSLs is used solely for VoIP connections - where remote users have IP phones that connect into the corporate PBX via the Internet. Last week we had to do some remote management on one of the users' desktop PC, as it was starting to run weirdly. This meant going through the rigmarole of getting her to run up a browser connection to her ADSL router's management GUI, find the right page, and read off the current (dynamic) IP address.
Then a colleague had a brainwave: let's set up a dynamic DNS entry via http://www.dyndns.com/. For the uninitiated, this is where you define a hostname and have a little application on your PC that updates the DNS regularly so that even when your address gets dynamically changed, the DNS catches up within a minute or so.
It worked a treat, and so if that user needs support, we just need to run up VNC and point it at her hostname - no mucking about getting her to look addresses up. It's proved so useful we're rolling it out to our other remote users now.