What's up with the Canon EOS 1D?

I had the chance to play with a EOS 1D at work. I noticed it was pretty old (2001ish) and thought I should be able to pick one up for cheap.

I go search for it, and the few places that have it want $700+ for it - sometimes just the body. And it's only 4.15 megapixels.

So, someone who knows their DSLRs, please educate me. Is this a collectors item? Is it that good a camera? Do DSLRs just hold their value for a really long time?