What happens when your email account gets compromised and the attacker uses the "forgot my password" feature on each site?
If you say you use multiple email accounts, then you can also use multiple Persona accounts. In fact, support for multiple accounts is part of the plan.
Like any sensible person, all my security question answers are of the "Correct Horse Battery Staple" type.
I don't see how introducing a single untrusted third party, many accounts or otherwise, is better than using a couple of trusted third parties such as gmail and hotmail.
The goal of Persona is that you should be able to use Hotmail and Gmail as your trusted identity provider; the current system is just a stopgap until there's more support from providers.
If you say you use multiple email accounts, then you can also use multiple Persona accounts. In fact, support for multiple accounts is part of the plan.