I'll guess I'll answer a few of these since I'm sitting at precisely "close to 4 thousand".
I try to buy primarily on sale, whether its great used sales at a local FYE, waiting for B&N Criterion sale, or just finding the cheapest place to buy from in general.
I started collecting while I was still in High School, so about 8 or 9 years ago. My wife kind of hates it but she isn't too hard on me about it, though some times she can be.
I've taken several breaks over the last two years though from buying, up until actually a month or two when I picked it up back again.
Here's my collection: http://samsanch3z.dvdaf.com