I honestly don't think that I could use a Mac without TextExpander anymore. I have a customized list of "frequently misspelled words" that I have it correct for me, as well as a snippet of text for creating a new shell script, a shortcut to insert the current date or time, HTML markup, and more.
TextExpander has been able to sync via MobileMe for some time, but version 3 also includes the ability to sync via Dropbox. It can also correct "double caps" at the beginning of a sentence which happen when you accidentally hold down the shift key for too long. There is a feature to capitalize new sentences as well, but that feature was a little hit-or-miss for me.
In its new application form, TextExpander has to be running for it to work. That may seem obvious, but since it used to be a preference pane, users may be used to it running "hidden" as a daemon in the background. There is an option to hide the application icon in the dock. If you hide it in the dock, you can still access TextExpander from its icon in the menu bar. They've even included several different styles of icon for the menu bar, which is good news for those of you who believe that menu bar items should only be black and white.