Business account for 2+ years and it of course was needed with the amount of transactions going through it. Never had an problems with Paypal had a few disputes on the account but that is about it.
How to downgrade to personal is explained somewhere on the support pages. I think you have to email them about it (don't remember exactly).
I think they should allow you to have a personal balance and a business balance in the same account. Different e-mails/bank accounts all in the same account. Just a bit more orgonized I guess..