I once abandoned a piece of land, actually. It was a lot that I got with another lot in a subdivision, one of which I really wanted to build a spec house on and figured I'd just build two while we were at it because the developer gave us a great deal on both lots (basically two for the price of one discounted lot) since they were the last ones left and he wanted to be done (it was a small subdivision and it was his first one).
The first lot was fine--we built and sold a nice house. The second lot, however, was essentially not buildable thanks to the grade, a creek, and the shape of the lot. The neighbors didn't want to buy it, so I listed it for sale. It just wouldn't go, so after a few years I just quit paying taxes on it and let it get auctioned. It was in the next county, I'd already made my money on both lots through the sale of the spec house, and this all started in summer, 2007 as the bottom fell out of the credit market, followed of course by the crash of 2008.
That was my first spec house and many lessons were learned, so I chalked the money for that lot as "tuition" and have moved on with my life.
The strangest thing about that is, I have no regrets about just letting it go. In fact, finally making the decision to do so was a great relief, like a burden was lifted. I guess I didn't realize how much owning a worthless lot was bugging me.