I spent a few summers in America in the nineties and never overstayed. I was going there again last year for the first time in almost ten years and got stopped at immigration in Shannon. Terrible experience - they grilled me about dates of entry and exit from ten years earlier, what I had done when I was there, why I went, why I came back, what was I doing now, etc. I had to lie about working there as I had no visa and was working illegally at the time so was very nervous about that. Just before final boarding call they said I could go through but that they would be marking my passport in such a way that I wouldn't be able to travel again until I got clearance from the American Embassy in Dublin. The immigration officer made it very clear that she could have stopped me if she wanted. I made an appointment at the US Embassy and had to bring along documentation such as College transcripts from the time that proved I had been in Ireland and go through another interview where the emphasis seemed to be on my ties to this country now.
My advice to you would be to get this sorted before you book a trip abroad. Don't ignore it and hope you won't be affected. The stress isn't worth it. It took me about six weeks to organise the appointment at the time so get started on this today.