not bad, not bad.
now, the things that I would suggest are:
1. Make a walk away button.
This way, you can make a scoreboard and people can compete
against eachother. Thus making your game thrive.
2. Make it a little harder.
If you add like a 5th cup or make the randomization a little
faster, then it'll be a little more challenging.
3. If you don't care for the "Walk away" button...
...I'd suggest having an unlimited amount of rounds, and just let
the players keep going until they lose. This way, you can still
have your game thrive with a scoreboard feature, and
completely eliminate the "betting" system alltogether.
Other then that, you've got a smooth game, and it's very addictive.
Keep up the good work and you're bound to make something that'll land front page.
Peace
Eyseicle