Back in the beginning of 2007, my company switched from a twice-monthly paycheck to bi-weekly. Due to the way they set it up, the first paycheck was only for 40 hours instead of 80. (Despite the fact I am salary, we still have hours in the paycheck. Don't ask me.) To make up for this, my company offered an advance of 60 hours pay. The first paycheck under the new system would then be for 100 hours, and I would pay back a little bit at a time through August.
Of course, I took the advance - it was a free loan, with automatic payments and no interest. Then I forgot about it. Sure, I would see it on my pay stub occasionally, but I don't really scrutinize them because they're all the same. Until the paycheck I got last week. When I was glancing over it, I noticed it was a little higher than before. I was finally done paying my company back!
You cannot imagine how excited I was to discover that extra $57 in my paycheck. Although I should have remembered, it was unexpected. What a great feeling. That night I went home and recalculated my budget, debt payoff forecast, and expected interest paid. What a great feeling.