Tim O'Reilly has described the Internet as the new OS. Recent observations lead me to believe it's new the new Unix. Consider the following philosophy:
Write programs that do one thing and do it well.
Write programs to work together.
Write programs to handle text streams, because that is a universal interface.
This is the Unix philosophy, but it applies equally well to successful web sites. For example, I love del.icio.us, but it sure isn't for its clever domain name. It solves a simple problem well and doesn't get distracted by anything else. By also providing a useful API, it lets me manage my bookmarks in a number of different ways.
Recently, I've been using Twitter, and I'm honestly turned off by the user interface. However, because I can use my phone or IM client, it's still a useful service.
Although I haven't written about it yet, I've been using Dopplr for a while now, and I like it. It's a simple application that lets me keep up with my upcoming trips as well as the trips of my friends. It does one thing, and it does it well.