I have an acct in ING too. I use it for my irregular bills, house insurance, property tax, car ins....that kind of stuff. It takes about 2 or 3 days to have the money transfer back to your checking account, but that works for me. I never need it quicker than that anyway.
I keep my Emergency money (6-8 months expenses) in my MOney market account, because the smallest check you can write on that acct is 250.00.