Fish, I get the impression that you deal in real money ... why have a checking account at all? Open a CMA or AMA type of account and get a decent interest rate on your rolling balance, plus generally better service than the fork-and-spoon technicians get from the bank tellers.
The most compelling reason to have more than one checking account is if you suffer from the chronic condition known as marriage. I have loved many women in my life for various reasons and at various levels, and I don't consider myself sexist, but the sad fact of the matter is that I have never met a single woman -- from my mother to my current wife -- who was not able to easily outspend any level of income to which she had access. My current wife went years with -0- idea what our financial situation was, right up to when we had our first kid, at which point I sort of had to clue her in. Before that we had a reasonably nice lifestyle paid for with about 15% of my income. Now we have a fucktard McMansion lifestyle that is setting me back a solid 30% if not more. Thank God for the Cayman Islands.
Anyway ... aside from hiding money from your woman I would say that any account that is used to reup or withdraw from Neteller or PayPal should be "dedicated." Ditto any account used for online billpay, direct debits etc. This is simply a security and privacy measure ... security and privacy are imperiled by EFT/ACH transactions, as well as by automated debit programs, so it only makes sense that if you are toting around any real money, you don't want it sitting in an account to which some dildo at BoA or PayPal or wherever has the number and contact info.
Phaedrus