I regularly use four separate accounts. Besides the standard personal and work addresses, I have an ancient account that's dedicated to things like registrations, purchases and subscriptions, while another is solely for times when I'm not comfortable giving out the others. All of them are funneled through a single Gmail inbox, which makes it easy to keep tabs on everything.
What about you? How many accounts are you actively using and do you prefer checking them through a Web interface or a desktop client like Outlook? There's a poll eagerly awaiting your mouse click after the break, but don't be afraid to leave a comment, too.