I remember someone on this site, in another topic, saying the DualShock controller is like Mario in MarioKart: good, solid all-around, and versatile.
That said, I prefer Yoshi.
Yeah, the controller has a pretty storied history, and I've had some of the best gaming experiences with that controller in my hands. But Sony could learn a lot from it's competitors to polish away some of it's blemishes.
In general, I'd like to see it gain a little bulk. Not weight so much, but bulk; especially after feeling how comfortably the GC and 360 controllers sit in my hands. Just more ergonomic contours on its underside.
I'd like to see the L2 and R2 triggers given a little more concaveness. Not as much as the 360 controller perhaps, but a little bit more than it has now. One problem I have with the 360 shooter is that it works great for shooters and racing games, but I get handcramps trying to play NBA Street Homecourt with it. I can't imagine God of War working too well, for instance, with shoulder buttons that "trigger-like."
I'd probably like to see the left analog switch places with the D-pad too, frankly. it does feel just right, playing any game. And concavity to keep my fingers from slipping off them would be nice too.
I'd also like a slightly bigger PS button, and I think the Select and Start buttons should move up, almost next to the "Sony" label. Those buttons can sometimes be a little hard to find.
Beyond that, I wouldn't change too much, and I honestly wouldn't mind if they didn't change it at all when the PS4 comes out.
An aside, I honestly don't think the Boomerang concept was a design meant for serious implementation. It seemed more like an eye-catching kind of "future shock" design, meant to attract attention more than anything else. Anyone know if they were ever actually used at any conventions or private tests or the like?