Watch some WWDC! The presentations on CoreData are very good.
I don't think the introduction of Core Data on iOS (WWDC 2009) is publicly available, but they've had at least a couple Core Data presentations in 2010, 2011 and 2012 (all of them are freely available).
Is that hard technical docs or just demo videos? I get the most of the why of it, just not the specifics of the how (note: I am not a native iOS/Cocoa programmer - still trying to come to grasps with a lot of it).
DBKit is way more in line with what I'd rather do to use a database, than go thru a ton of abstraction.
CoreData is awesome because it persists the model (in MVC) automatically, and is fast; probably faster and more memory-efficient than 99% of SQLite codes out there that people write. And if you have complex object graphs (for example, a vector graphic app with layers and shapes or something like the excellent "Pi Cubed" app) it's really, really hard to do it without CoreData (maybe an order of magnitude more code is required). But if your data is simpel, or easily represented in a relational way with simple keys, maybe SQLite or DBKit are easier (but probably not faster or as memory efficient).
