This article has the most information about the specific effects of the Spellplauge in Forgotten Realms that I have seen to date. It is well worth the read.
Check out this new article Wizards of the Coast posted recently:
Countdown to the Realms: Magic in the Forgotten Realms
Magical power and fantastic features abound in the Forgotten Realms. If fact, the Realms are so awash with magic that the world proved particularly vulnerable to a plague that fed on magic itself.