Suggestions for Performing Regression Testing?

gmletzkojr asks: "The company that I am currently working at develops a fairly complex industrial controller, complete with embedded software, a GUI on the controller, and a Windows app to connect over Ethernet. On previous versions of a similar project, we have performed testing manually - ie, monkey presses button, and sees that light turns on, widget turns, GUI updates, etc. However, this is extremely time consuming (previous complete regression testing took ~3 weeks) and is error prone in itself. How do you perform complete system regression testing? Do you use shrink-wrapped packages, or build your own? How do you test features that are easy for humans to observe, but not as easy for software to detect (ie, the light came on, the GUI updated when I pressed the external input, etc)?"