Well, the difficulty curve is in that each day the limit you have to earn goes up. I got to day 25 when I hit a "wall" which certainly was partly because of buying decorations that don't pay off or not enough.
Speaking of decorations...
The first page is clear in what you get back for them. On the third page the "add one more table" is also clear, but what do the popularity things do? And have any of the decorations from the middle page any effect?
As for bugs... I don't know if the main menu background should be fitting to the screen size or not, and there didn't seem to be an "official" Quit button...
It would also be useful if one could access the shopping window from the "day finished" screen, so one wouldn't have to first start the next day to then go to pause mode.