You should Definitely start using the -native and -bundle flags in your windows/mac builds, that makes it so much nicer for your users (the disadvantage being now you have to package several binaries rather than just one air file). This is exactly what you want to do for Steam, however, b/c it requires ZERO installation. You just have a folder with an executable and a bunch of dependent files in it, perfect for Steam. This is how Defender's Quest, Offspring Fling, and a bunch of other Steam AIR games do it.
If you want to wrap that in an installer for your direct customers, I can give you my NSIS scripts for that.
Ah yeah, that would be great! As well as the linux scripts too (I'll need to wrangle with that later!) I will e-mail you.