I think it is all interesting, but like someone said, I don't think there has been much since graphite. Maybe O-ports, hammer tech and string patterns (a la 99s), but I don't know that they revolutionized the racquet industry.
One breakthrough that I don't think has gotten any notice is PK's Kinetic system. Along with some other elements, it helped me get over TE. The really intersting part, though, is that it makes the frame very solid and stable. Volleys are very controllable with those frames. I was desperate to save my arm, and I wasn't buying the hype, but I took a chance anyway. Now I'm pain free and playing better than just 6 months ago. I have worked on my technique a lot, so it isn't necessarily the racquet, but I'm a believer in Kinetic. Revolutionary? Probably not. Evolutionary? Definitely.
PK 7G w/BHBR 17g X Weiss Cannon Silverstring 17g @ 54lbs