I write installers for my internal stuff. It helps me keep things uniform and I never have to wonder how a particular do-dad was installed. I can read the installer if I'm curious. My life got so much better when I started doing that.

-Pileofrogs

Update: A lot of folks are arguing about installers vs. no installers like there's only one way to do it. The important thing isn't that you use a whiz-bang installer technique, or even that you use the same technique on all your stuff. The important thing is making your stuff with a reasonable installer.

For example, I might build a perl module with one of the made-for-CPAN tools, or I might use make to run a spell checker on my HTML web pages... Either way, I know when my stuff is up to date.