I made my first offer recently. With pretty conservative (0% appreciation over 30 years, 1% inflation) calculations it is net neutral to positive over our rental situation the last few years. There is a pretty good chance of getting it net to us.. zero down. So the basic calculations were that we don't have to put a lot into the place, we like the area and if everything goes to heck the bank has a nice shiny well kept house to market.
I won't provide too many more details, as many know I am extremely private. But I thought it'd be a good topic for discussion.