I'm one of those people who goes treasure-hunting in the iTunes store, builds up a long wish list, and then buys a whole bunch of songs at once. When I do this, iTunes divides my purchase into several smaller, equal transactions (i.e. if I buy $100 worth of songs, they'll divide it into 4 $25 purchases).
I assume they do this so that they can charge multiple transaction fees. That's aggravating enough. What's worse, though, is that my bank's Fraud Prevention Services department inevitably sees the multiple identical-amount purchases, goes "Aha! Suspicious pattern!" and deactivates my debit card. I have to call them to get it turned back on.
This isn't a bad_service complaint about my bank. I'm actually glad that they're so vigilant about possible fraud, and they're always very nice about reactivating. I'm just hacked off at the iTunes people.
ETA: Many thanks to the folks who've addressed the transaction charge issue. I guess I just assumed that iTunes charges my bank a tiny bit of $ every time I purchase something, because I couldn't imagine any other reason iTunes would break up my purchase into multiple smaller purchases. Perhaps I can contact them and ask them to not do that.