In the past four years, I've learned the hard way about how painful it can be to try and update a codebase used by a large number of applications. Changes that seem innocent can break a specific use case that wasn't anticipated. Do enough manual regression testing and you will catch the bugs, but it's' costly and time consuming process. When things are costly and time consuming, they usually stop being done.
This is why I focus a lot of my efforts towards build process automation. Computers are fantastic about doing boring, repetitive work and never complaining. If you can get them to do the boring chores for you, you spend more time doing the fun, challenging work.
UI Regression testing is one of those spots where I'm looking for automation scripts to take over. Not only because playing "spot the difference" between your builds is boring, but also because [we're horrible at it](http://en.wikipedia.org/wiki/Chan