"If someone's going to go through all of the labor to make a copy of groupon or an iFart app or a twitter API mashup just for the cash, they should just write a Forex trading algorithm."
You mean writing one that makes money? That's infinitely harder than the examples you provided.
Quite a lot of smart guys put nontrivial effort into that. You need to be as good as them, preferably even a little better. Good luck.