Wow, what do you do with 10 accounts? Isn't checking all of them a hassle?
I have multiple domains and aliases, and Fastmail is much better at those than Google Apps ever was (I also have the free plan but you can never change your initial domain), so I'm much happier.
Several accounts are for separating services - AWS has it's own account, for example, so does Dropbox. I use a different email address for forums and such.
A few for friends and family as well. --Friends I can tell to pay for themselves if I need to, but family, not so much.
Edit: As for checking them, most don't get many emails, and every good email app can handle multiple accounts easily, so I get notifications on my phone.
Fastmail allows you to do things like stavrosk@dropbox.yourdomain.com, and then you can filter emails by that domain name. Lets you easily block out spam without having completely different email addresses.
I have six. Some of my clients ask me to manage their AdWords for them. Plus, I occasionally need to log in to my wife's Gmail account. (To confirm logins when paying bills, for example. Anything personal, she's smart enough to keep on her own domain.)
I have multiple domains and aliases, and Fastmail is much better at those than Google Apps ever was (I also have the free plan but you can never change your initial domain), so I'm much happier.