Incredibly vague question, I know, but I'm curious to hear about people's experiences.
traditional biologists are not mathematicians - they wont expect you to know much about computers, therefore you are "overqualified" at least in your area of expertise.
biology has a whole bunch of unsolved problems in areas like protein folding, that are basically problems in mathematics. in order to understand those, you dont really have to be a biologist, but if you spend a couple months studying the underlying biology, you will be good enough.
degrees in "bioinformatics" are popping up everywhere, because they need computer scientists who know a couple things about biology.
and you get to tell yourself that you are a small cog in the machine that works towards a world that is free of disease. if thats what you want to do, i'd go into biology.
how do you get there? apply for jobs. maybe rearrange your resume a bit in such a way that it says "numerical simulations" instead of "iphone apps".