I don't feel as though I was a good friend about it. I was tardy paying it back for reasons that I don't think are good enough - though mostly valid. I don't know how they feel about it, and they never asked me for the money (and it wasn't a huge amount, but enough), but I ate at me that I owed. If you're out there, friend, I'm sorry I was so late.
If you really feel badly about it, then add a gesture to your payment. A card, a six pack of their favorite beer perhaps or even some interest.
You shouldn't worry about it! By just paying him back, you've proved yourself a far better friend than a good deal of people. I mean, I, right now, owe like two of my friends money, and have for quite some time. So I guess you're better than me, at least. :)