The new integrated Playbook email client "Messages" was not loading and froze. My 3 accounts have disappeared from "accounts" tab. I restarted the device and my accounts reappeared but Messages seemed shaky.
My default account is Hotmail and I just found out that the Microsoft Hotmail servers were down since last night for many accounts. I changed my default to Gmail. It seems OK now.
I hope this can help anyone and that it was only a Hotmail problem.