I've got three questions here. Two that's been bugging me ever since I bought my Les Paul, and one that's bugged me for not that long.

First: What is the difference between Alnico Pickups and Ceramic Pickups? My SG and ES both have Alnico Classic Pickups, while my LP has Ceramic 8 Pickups, and I have absolutely no clue what the difference between the two types of pickups is.

Secondly: What is the difference between "open-coil" and "closed-coil" (or "shielded" and "un-shielded") Pickups? My local guitar store usually only has open-coil Ceramics and closed-coil Alnicos on their guitars, which leads me to think that Alnicos need that shield to sound proper, while Ceramics can apparently go without, but they sound pretty much the same to me. Does the shield make a difference in the sound the guitar makes or is there some other reason to have it there?

Thirdly: What does it mean when a Pickup is "hot"? Christopher Schlegel mentions the term in one of the first lessons in his 70's Arena Riff Rock tutorial.