I thought the main reason to use a debit card was so you (and the cashier) don't have to bother with change! 
I guess we just have to agree to disagree. If I was using this for my primary savings account then yes your points are very valid, it does have a horrible interest rate. I like to use it not because it forces me to save. I do that on my every 15th of the month with my ING. But because I use my debit card all the time on basically 99% of my purchases and feel this is great way to build up some extra money. two months ago just from doing the keep the change I actually earned or put away $90. I just like it, it a fun way to build up some disposable income that I can transfer into back into my checking account to pay bills or transfer it to the ING.
I must admit I was laughing about the comment of your mom getting excited about grabbing a penny