I've heard Astronomers talking about backlit CCD sensors, and talking about how much better they are than other types. What are they, why might I want to get one, and what are the pros/cons of this compared to related technologies?
A backlit sensor isn't really a new kind of sensor, it's just a different arrangement of the imaging elements to allow more light into the sensor. From Wikipedia:
They're not without issues though:
Backlit sensors improve the low-light performance of a CCD chip, reducing the ISO needed for low-light conditions (and thus reducing noise). This is a clear benefit to astrophotographers, allowing them to use shorter exposures with less noise to get equivalent shots.