Metro is the name of the design language for Windows Phone 7. If you've been paying attention, everyone (who's "on message") has been saying that Windows 8 is "metro-like" or "metro inspired" or the apps are in a "metro style".
Those suffixes are important.
This isn't just me being picky. There is an important difference to be aware of.
I've seen lots of WP7 apps which don't quite "get" Metro and as a consequence don't quite feel right or worse still feel clunky or awkward or not as intuitive as a good app should or worse still don't work as expected, or like most other (including the built in) apps on the phone.
If you approach Windows 8 app development assumming it'll be exactly the same as Windows Phone 7 then you risk making a variation of those same mistakes and creating more sub-standard apps. - The world already has more than enough of them. We don't need any more. Thank you.
There are aspects of the Metro design language which are specific to the phone context:
"Focus on the individual"
"Relevant ... to your location"
These are primarily phone based characteristics.
I say this is important because I don't want you to get carried away and start thinking that you should recompile your phone apps for Windows 8 just because, in principle, it's simple to do, and just because you can.
Hopefully you've designed and built your Windows Phone 7 app to be the best it can be and to be perfectly suited for use on the phone and make the best of the platform and the screen real estate available to you. - Such an app doesn't necessarily directly translate to running on everything from a 7" tablet to a 30"+ PC monitor.
So what's different on Windows 8 when it comes to metro-like/style/inspired apps?
- Think "touch-first" but don't rule out and remember to support Mouse (& keyboard) Events.
- Embrace the touch language and don't deviate from it.
- Be prepared to scale across different screens.
- The experience should transcend the process.
- Take pride in craftsmanship
- Do more with less
- "Win as one"
Expect more information about creating metro style apps to be released and made available over the coming months and be sure to check out the videos from BUILD on Channel 9. Especially the XAML related sessions (as identified by Tim Heuer).
If you've built Windows Phone or Windows Store apps you can cross-promote them with AdDuplex to get more users.