You got a million roses? How did you do it? I get bored to easily.
What happens when you get a million?
The little spinning star on a couple of loading screens becomes a little spinning rose, some roses grow in the stage-select meadow, the title screen changes from We <3 Katamari to A Million Roses (I think; it might be One Million Roses) and a bonus track appears in the sound test. It is not much reward for a long and boring thing to do, but then again you weren't promised anything special.
Also, as you increase your rose count the King expresses increasing degrees of disbelief in your patience, the lonely rose gets bigger and its dialog changes some.
As for how I did it, I confess that I only actually got about a tenth of the roses myself. Mostly I reloaded the stage until it came up the ice rink, rubber-banded the joysticks into position, and left it running while I was doing other stuff on my computer. Since I didn't want to miss any messages, I didn't leave it running overnight, but if you do that it'll go faster. This method is considerably slower than rolling up all the roses yourself but is much less likely to make you curse the heavens.