The trick on the doubling, Graham, is to know exactly how far you are ahead (or behind). In rolls. If you double when you are looking at a certain or near-certain gammon, your opponent will cede one game instead of losing 2. You're doing them a favor! So you can't be TOO far ahead.

I've got a little pocket backgammon game given me by my XMIL, and it doubles far more often than I do (I never think about it!). So over many, many games (it usually beats me about 60% of the time) I've kind of gotten a "feel" for when to accept a double and when to cede the game.

Unfortunately the machine is really stupid when it comes to rolling off. Whoever programmed it wasn't terribly sophisticated in his (or her) end-game.

Alex