I have paid almost all of my bills through direct debit and I think it's a great service. I happen to earn a substantial salary, so I'm not usually concerned about my bank balance running low during the month. I just like the convenience of not having to worry about paying the utility or cable bill every month. I know when my mortgage payment and car payment will be made.
The only con I've experienced since i started making direct debit payments is the tendency to overlook the other obligations from time to time. I'll sometimes forget to write a check for a charity organization or a local store that doesn't accept direct debit payments. Since I'm not sitting down at a table writing check after check anymore, I need reminders that a few bills are still unpaid.