1. For this to take off, other providers would have to implement the Wave API/protocol. Other providers like Microsoft, Yahoo, Facebook, etc. Just as today ever

1. For this to take off, other providers would have to implement the Wave API/protocol. Other providers like Microsoft, Yahoo, Facebook, etc. Just as today everybody is running SMTP servers. 2. What does open-sourcing mean? Is Google open-sourcing their server-side code? Probably not, since it's tied to the Google architecture anyways. Implementing these APIs/protocols would be a significant expence for the other providers. Also, open-source or not, this would still be a Google-technology (controled by Google), and large corporations don't like to invest in other's technology. 3. Presumably Google would allow Gmail users to upgrade with a click, so they'd have a good amount of seed users. But still, most of my contacts are not @gmail.com, so the experience would be limited. 4. This probably includes email as a special case, eg. your Wave provider is still running SMTP servers and receiving email messages coming to your address (Wave address = email address) and placing them in your Wave inbox, and sending out emails per SMTP if the other side is not Wave enabled. This means painless upgrades in terms of "compatibility" for the user. Correct me if I'm wrong, I've only skimmed the docs!