Back up your data, people. It's so easy (if you've got a Mac, anyway).

Thanks for the encouragement. I decided to do this after reading this and other comments here, and yes it was easy. I used a portable hard drive many times larger than the Mac's internal drive, dedicated just to this, and was guided through the process when I plugged it in. I did read up a bit on what it was doing but was pretty satisfied that I didn't need to change anything.