I check my library card online every day.
Sometimes many, many times a day. In fact, I was just there.
I'm checking to see if anything I've reserved online has come in to my branch. I'm checking to see if I have any fines, or if JEM has racked up any fines on my card. I'm checking to see when my books are due, etc.....
I'm not sure what I check more, my e-mail or the public library website.