Good question. I searched around and I could not find much. I drilled around for a while on the Struts site and found a detailed list of changes for the first 1.2 release (sorry I don't have the URL) but it was too detail to get a feel for what changed.
I am using Struts 1.1 and I felt like I was missing out on some cool new features of 1.2. Are there some cool features in 1.2?