Two examples of Anglo-German alliance from recent live gunboats:

1. I played the English side of the alliance to a 3-way England, Germany, Turkey draw in http://webdiplomacy.net/board.php?gameID=171383#gamePanel. The Anglo-German alliance was rock-solid from Spring 1901 on, and Germany built no fleets the entire game. I had the upper hand for most of the game and could have possibly stabbed Germany for a solo bid, but decided not to as a five-way draw or Turkish solo could have ensued.

2. I played the German side of the alliance to a solo win in http://webdiplomacy.net/board.php?gameID=171745#gamePanel. England and I made rapid progress against both Russia and France, but I was benefitting the most from the arrangement. England then stabbed me in Holland & Belgium. So I allied with Russia against England, then when Russia got too big I re-allied with England against Russia, and finally took North Sea when England wasn't looking for the killing blow. I only had two fleets at the point I stabbed England, but I feel you can stab England as Germany with as little as one fleet as long as you can take North Sea (assuming a commanding land presence as well).

I just got my first win playing Germany on this website in an alliance with England, game name Normal Diplomacy-7.
I think it's more common for England to backstab Germany in this alliance.
I was lucky because I had a loyal ally, and his movement into Mediterranean was a bit delayed. It ended well and it was a game with that allegedly "horrid" ppsc scoring so player with England did OK points wise

I think it is easier for England to do the stabbing in this alliance than vice versa. It happened to me recently. I think Germany has to insist on building a couple of fleets. If this inspires England to attack Germany, they probably would have stabbed later anyway.

In response to your post, Amwidkle, I played England (as you know), but it was my first game as England. Inexperience drove me to do things that I should not have. Plus I was so worried about a Turkish solo that I moved my units from attacking Russia to blocking Turkey that I exposed myself to a stab. I didn't see it coming, if I had, I would not have used my fleets to block Turkey.

Also, the fact that those games are live games implies that the decisions each nation makes are impulsive and usually without strategic (far future) planning. Or maybe this is just me in live games -- I can't speak for anyone else.

That's certainly the case for me in my live games:-)

I actually think this alliance is better for Germany than England.

From what I have seen the England player always has trouble resisting the temptation to go to war with Russia, who is often busier in the south... but will still probably feel compelled to build SOMEthing in StP as early as they can afford to. And so the arms-race begins.

And since the Anglo-German assumes "versus France" (otherwise it's a Western Triple), this means England probably has two fronts very early on and needs a huge string of fleets to supply it. If we assume the Anglo-German gets both partners to 7 SCs, an England with five fleets and two armies is not as well-positioned to stab as a Germany with five armies, two fleets, a pink France and a wide open Russian heartland.

I think for this one to last past the fall of France, England needs a better relationship with Russia than Germany has been able to achieve, peace in Scandinavia, and two, if not three, armies on the continent.