The Federal Trade Commission has required one large collection agency, Asset Acceptance, to start informing debtors when the statute of limitations has expired. Not all collection agencies will do this, but you do have the right to ask if the statute of limitations has passed. And if the agency responds, they must answer truthfully.
If you're served with a lawsuit summons, it's best to contact an attorney with experience dealing with creditors and debt collectors. That way, you can be fully aware of your rights and have a legal representative in court.