I have a free checking account and a savings account. Now at my bank, savings accounts are only free if you have a checking account, and agree to have them move $25 from your checking to your savings every month. OK, fine.
But for SOME reason they would not move the $25 every month. Some months they did, and some they didn't. And it was never on a specific day, always just random. So I never knew if or when the money would be moved.
Well one time it really screwed me over, because they moved the money when I had less than $25 in my checking, causing me to be overdrawn, thus causing an overdraft fee. I had no pending transactions, and was getting paid that day, I just wouldn't make it to the bank until the next day. So that really sucked.
The bad service here is really that they said this would happen EVERY month, but sometimes it would go three or so months without moving the money, and it was always on a random day.
Luckily, when I called to sort it out they were nice and removed the ODF and I told them to move the money on the 19th of every month, the day after I know I will have money, and it has worked that way ever since.
But damn that could have been messy.
ETA: I didn't have them schedule the transfer right away. The same thing happened a couple times and each time they did reverse the ODF(though sometimes were snippy about it), until finally I asked "can I have you re-set the transfer and schedule it for the 29th of each month?" and they did. The customer service reps were fine for the most part, but the whole screwy system thing was bad service IMO. Additionally, they should have asked what date to schedule it when I set up the account.