I know that a lot of self-employed people are tempted to not report cash income on their taxes. In the past, when applying for a mortgage, you could get a "no doc" or "low doc" loan, meaning that you could qualify for a mortgage based on your credit score, without having to prove your income.
However, the story is out today that the fed is planning on banning these types of mortgages, meaning that you will need to provide proof of your income (copies of tax returns)to get a mortgage.
Something to think about when doing taxes this year. If you're income looks low, you might not get that mortgage. Story here:
http://www.msnbc.msn.com/id/22309285/