Entrepreneurs tend to remain in the business arena they came from. Some are alumni from companies that would be a competitor to the enterprise being created or joined. And some are former selling shareholders of just those businesses. What is the rule about those pesky non-compete agreements signed upon discharge or sale of the previous company?
The good news is that if you were not a significant (usually 5% or more) selling shareholder of a previous company, many states specifically exempt non-compete agreements signed between companies and their employees or minority shareholders. In that case, you must worry only about information and trade secrets taken from the previous company which are both certainly subject to protection by almost all laws and courts.
So, to everyone: do not take customer lists, design documents or any document considered a trade secret from any previous employer or previous consulting customer. Yes, some companies were sloppy and did not have you sign a confidentiality agreement, but that procedural slip does not protect you from their legal wrath. Further, there is no expiration on these documents. You cannot complain that the document or information in question is more than five years or two employers old.