My walmart's fluorescents do the bright/dim thing with the daylight too, and when it gets bright enough they'll just kick off altogether. Seems to happen sequentially starting from the middle of the store and working to the sides bank by bank. When they kick back on the opposite happens, they start from the sides and go inwards...its actually kind of cool to watch. I would say they have it dialed in pretty well because unless you're actually looking at the lights the overall brightness level in the store seems to stay about the same...but of course us light guys notice such things
One of the best things they've done though is switch out all the soft white bulbs for daylight ones...it was part of a huge remodel they did a couple of years ago. Before the switch I would say 40% - 50% of the lights in the store were dead or dying, it looked nasty.