Hey Holden. Best answer I can give you is: [quote=Cormyn] if we can get some of these bugs squished this week, I'll send out the invite codes. It's a significant enough number of users to warrant holding off until some of these bugs get fixed first.[/quote]
I guess once the Activity Stream has had its week of test drives, the team will send out more invites. I'm not sure if its because too many users will give duplicate feedback or if too many users will cause a strain in the AS, but it looks like newer beta testers will have to wait until they are ready. You can ask Cormyn for extra details, if you want.
So far, I haven't encountered any bugs on the Activity Stream itself. Actually, I don't think there have been any reports! The AS just needs to be better. I'm sure the team will immediately send some invites once the AS is tweaked and perfected.