I can spend MAX_AMOUNT_IN_BANK, but I can only withdraw $40 from a machine per day.
I use it at school, work and at restaurants that I trust, but nowhere else.
My school doesn't take credit or debit. The concession stands (yes, plural, I work at a big place) at work accept them though, so that in combination with the employee discount equals pwn. So far I've used it at work, Walmart, and McDonalds.
About the only place I use my debit card is at the ATM. I hate using it to purchase stuff. I just withdraw money and have my mom buy stuff on the internet.
Sad, because she uses Windows, and there's a good chance a key logger will get installed and it'll eventually steal her password long before any site does.
I don't see any reason to use an ATM except for depositing, and I don't even know if they support that anymore (they used to, but it was always out of order, 24/7/365).
Also, Windows is relatively safe, if you know what you're doing. The fact is, though, that nearly everyone doesn't.
* Joe[x86] agrees.