This is a very cool thing! I'd like to write an article about it at Google Earth Blog. But, I before I do, I'd like to make sure you feel things are working smoothly.

I have a few suggestions (in case you haven't already thought of these):

1) Maybe updates every 10 seconds is too frequent. Other people who have had fast updating dynamic updates have found when dozens or hundreds of people simultaneously view them the bandwidth on the server goes through the roof quickly. Recently a couple of sailboat races were being followed with GE and they had to greatly reduce their updates to like once every 6 hours. One suggestion I've seen is to force people to do a manual refresh. This way if someone walks away from their computer, it won't be hitting your server for no reason.

2) Your format should definitely be KMZ if you're not already doing this. It compresses the data.

3) Why not use the built-in airplane icon? This would save a bit of bandwidth since you wouldn't have to send the image each update.

4) The track altitude data seemed whacked when I looked at it. Sometimes it was at altitude, sometimes it went below sea level. You might want to make it relative to ground instead of absolute. Or, just check the data. Maybe its a problem with your source?

Great work guys...let me know when you're ready and I'll write a story about it.