OK, we just finished the first closed test and it was an spectacular success, though not quite in the way I was expecting...
First off, the server crashed with a totally inexplicable NPE just before the test - not a good omen! I stuck a band-aid over the place and restarted the server. No further problems.
My co-tester, Mick, was half a mile away on a linux machine, I was using XP.
We started the test and all went well. We could both see each others units moving around. Though the ping was really bad (~500ms) the game was designed with this in mind and still ran smoothly. On to testing the chat system. Press 't', type chat and press enter. Flawless. Then disaster struck! Mick forgot to press 't' before typing a message. Unfortunately I'd forgotten to disable the hot-keys I use for testing, so when Mick hit the 'n' key a new enemy village began spawning right next to us and started attacking us. Despite using another hot-key to instantly spawn units we both ran out of gold pretty quickly and had to fight hard to keep them off. Then some bears attacked. Mick fled with his 6 remaining archers - straight into the path of another enemy's cavalry troop who'd come over to investigate. Doomed! I wish I'd videoed it now, it was very entertaining!
There's plenty of flaws in the thing still, (the most annoying is the way it gives you an extra king every time you log on) but overall I'm pretty pleased. It seems stable and playable.
My biggest worry was the quota usage. Setting up and running the test used a whopping 6% of my daily bandwidth quota. Admittedly most of that was the repeated ~5MB download of LWJGL, the game and its resources. This a problem which client side caching should much reduce when I enable it.
My CPU usage was 3% of daily quota for a fairly short test. This is a much bigger problem to fix. There's a lot going on in the game so it needs a lot of CPU, but I'm not going to worry too much. I wrote the code for clarity rather than efficiency so I'm sure there's a lot of optimising I can do. If I really have to I can buy more quota anyway. Let's hope it gets that popular!