This is insane in so many different ways.

1) Why would you use floating point instead of fixed point or other fractional representation (uh, percent?) for this sort of thing?

2) Why would you design an interface that's specifically set up to make progress bars stall at 90%? This is insanely user hostile -- there are great UI patterns for expressing indeterminate progress when your progress is indeterminate!

3) Why in the example would you prompt user interaction at 90%? (I'll give them credit for at least comparing to 0.9f instead of 0.9 here.) What user expects a prompt to appear before progress is complete?

trigger warning, lol