It depends...
On what I am using it for. Here is my list:
- one address for all bills and/or personal finance related e-mails
- one address for all on-line correspondences such as web forums, online forms, etc.
- one address for personal usage between family and friends.
- one account dedicated to Craigslist sales
- one address for my work Exchange account
- one account for a non-profit organization I support
- a me.com account that has been migrated to iCloud, but have never used it for anything other than Apple related communications such as Genius appointments, iTunes purchases, etc.
- One other that I use for just communications with my ISP.
Other than the types specifically mentioned above, these accounts include both ISP provided and Gmail accounts. The worst part of my ISP accounts is that they are still POP3 accounts so when I delete an e-mail on my ISP account, I still get it on my Mac and iPhone.
All in all I have about 8 e-mail accounts on my iPad. I have considered migrating some of my usage to my me.com account (especially since my ISP accounts are still POP3 and difficult to manage across multiple devices), but I have yet to do so.