I like having Slimes more commonly, but with the new super flat world generation, slimes are spawning like mad, and whenever i try to kill them with my sword i break blocks... and since slimes have virtually no spawning limitations anymore, they are about the only mob spawning because of the map generating so low. And I have tried setting the difficulty to peaceful but i can't spawn hostile mobs when it is. Notch should add some limits to slimes spawning, or change the generation code, there is litterally swarms of slimes that are really difficult to kill, and when you do, more spawn! its crazy!
An easy solution would be to change a superflat world to be above layer 40 (or whatever is the highest level slimes spawn at). But I am guessing they chose to have superflat start at the bottom to give the maximum room for building above.
The point of the super flat world was not to have hostile mobs and try to survive, it was to build things more easily, in which case you want to be on peaceful anyway. Those who decided they WANT to try and survive on a super-flat world have to deal with the slimes.
Super flat world generation.