If you receive a notice from the IRS, the Department of Revenue or any other government agency for that matter, DO NOT IGNORE IT. These notices can be scary and they often threaten painful consequences such as a wage garnishment or a bank levy or seizure of assets. Generally, these issues will not just go away (although there are some statutes of limitations). Clients come to me frequently with notices that they have received weeks, months or even years before.
The problem of ignoring notices, in addition to interest, penalties and increasingly aggressive collection tactics is that, often times, you will lose rights as time goes by. The most important right that you can lose is the right to appeal your tax assessment. In many cases, if too much time goes by, the only card that you have to play in dealing with the government is to try to just negotiate the best possible deal.
Whether you call me or someone else or decide to handle it yourself, do not ignore these notices. Address the problem and you will almost always be better off.