I don't have ADD, but lots of the symptoms of ADD are also present with other disorders (depression, bipolar). Even if you never seek a diagnoses, treatment, medication, etc. there are a lot of resources for coping skills and ways to improve focus, listening skills, etc. You can look for a time management or communication skills course, even an online forum or something, to help you out.
If it's really affecting your day-to-day life, you're struggling with work or your personal relationships are regularly strained because of it, I'd seek further help (not necessarily meds, but counseling or a coping skill class)...however, if it's just a minor inconvenience, you can probably improve it yourself.
Also, things like a poor sleep schedule, poor diet, etc. will definitely make it worse.
I know a few people who have started on ADD medication as adults. Most of them, it didn't last very long, and wasn't worth the side effects. But, I do know one person (who was always a good student, successful young man) who's life drastically improved after he started prescription ADD medication. Since he's started, probably about a year ago, he's lost a great deal of weight by healthy eating and exercise, taken on various projects with success, and his already-good grades have improved, as well as his social life. He's never been in any kind of behavioral therapy, so it's safe to say the drugs are what's made a difference, but I don't think that's the typical outcome.