Lifehacker has a simple look at how to set up Mountain Lion's built-in text expansion (or, as Apple calls it, "substitution") options. In System Preferences, under Language and Text, you can go in and set up any number of text shortcuts that will expand into commonly-used phrases and words.
There are a few built-in already -- typing "(c)", for example, will give you a copyright symbol. But you can put anything in there, so you can use a few quick keys to punch out your email address or phone number, or use some other phrase for anything you happen to type often.
Developers know how helpful this can be while writing code. Not only can you use text expansion to help reuse bits of code, but a text expander can remember the exact wording or form of something that you might not always remember.
Third-party apps have handled this task well, but with the new restrictions on sandboxing, which is preventing a lot of apps from working on a system-wide scale, it could be helpful to set up your text expansions in the OS.