It's perfect the way it is.
No it isn't, and I get sick of seeing people say this. The Dualshock design is 15 years old, it's archaic and should have been retired at the end of the PS2 era. You may not have any issues with it, but every single part of the controller has long since been surpassed - if Sony actually had pressure to pull their finger out and create something new we could well end up with the best controller on the market. Even Nintendo has taken the hint that their designs don't cut it any more.
1: The ergonomics are woeful in comparison to the 360 and Gamecube controllers.
2: Analog sticks are the primary control method nowadays and should be treated as such.
3: The "triggers" are absolutely horrible - they go from having no resistance to being far too stiff and the shape means your fingers will slip off at times.
4: The segmented D-Pad is imprecise and rubbish at diagonals, it sucked compared to the Saturn D-Pad back in 1997 and it still sucks now. Even Sony themselves have done better with the Vita's D-Pad.
5: Sixaxis is an unnecessary expense, the price for the controller has doubled since the PS2 era and unwanted tilt sensors are not helping.
6: The grips on the analog sticks are inadequate and have a strange flaw where a clear liquid starts oozing out of them if left unused for a while - either more grip (ala the GC controller) or a concave design (ala the new 360 controller) would be better.