I'm familiar with Diplomacy, its rules (though don't ask me to resolve a set of conflicting orders right now) and some of the history of the game but I never played it. Was somewhat curious to try but I always hesitated because of the potential time investment.
For those interested, this site has some nifty materials and all the different rules including the Avalon Hill booklet for the 2000 edition :
http://www.diplomacy-archive.com/home.htmIn short, Diplomacy is a game played on a map of Europe divided into provinces by 7 players, each representing one of the great powers of Europe in the nascent 20th century (UK, FR, GER, AUS, RUS, ITA, TUR). Each player start, IIRC, with one naval unit and a land army. A number of "supply centers" (30 ors so) are disposed on the map and the goal of the game is to try and control over half of them (or the most, if total victory is impossible). The number of supply centers you control translates 1-1 to the number of units you can field (you can only build a new fleet if you take control of a port, etc...).
Each round, each player writes down the marching orders for its units, all orders are opened for everyone to see once its done and units are moved accordingly. No two units can occupy the same space, units can only move to an adjacent province and units are not destroyed in battles (they're only dislodged or blocked from a province depending on the rules to resolute all simultaneous orders).
What sets the game apart is that in between each order phases, players are entirely free to discuss with each other, either at the table or privately in order to strike deals, alliances or to convince someone that you're not moving your army on the Bosphorus straits. None of which is formalized into the game proper so you're equally free to openly lie or to suddenly turn on your ally (one of the legendary anecdotes has been about players bribing the post man to intercept and tamper the diplomatic letters of a fellow player...)
The mechanics are not too unwieldy. Some of the order resolution is a bit arcane though it's not too complicated (There's only 4 orders you can give : Hold, Move, Support, Convoy and the latter one is only for fleets transporting a land unit) but it's a fairly light game as a player can at most control 16 units. All the meat and potato is the diplomatic phase and there's no rules (except the agreement on how long it lasts) or chits needed for that. This means the game is very versatile and can be played on a board, by mail or a computer.
