Reinforcing my desire to run a Mystara campaign is a recent spate of blog posts about the setting:
There is Beedo's "Ode to Mystara" at Dreams in the Lich House.
Age of Ravens has reviews of The Principalities of Galantri, The Emirates of Ylarum, and The Grand Duchy of Karmeikos.
And I just discovered Darva Shriver's Stocking the Dungeon, which is all about Mystara and BECMI D&D. It's an awesome blog!