from
http://www.irs.gov/businesses/small/...122721,00.html
Will I Go to Jail?
A long-standing practice of the IRS has been not to recommend criminal prosecution of individuals for failure to file tax returns, provided they voluntarily file, or make arrangements to file, before being notified they are under criminal investigation. The taxpayer must make an honest effort to file a correct return and have income from legal sources. A letter from the IRS concerning taxes is not a notice that a taxpayer is under criminal investigation.
The IRS helps to get people back into the system as part of its long-term plan to improve voluntary tax compliance. The IRS wants to get people back into the system, not prosecute ordinary people who made a mistake. However, flagrant cases involving criminal violations of tax laws will continue to be investigated.