Google expects Google Play to drive more traffic and revenue to the entire ecosystem, including app and games developers. Google also explains there are almost no changes for existing users and developers:
Google Play is built on the same infrastructure as Android Market, so the transition for users and developers will be seamless. Users can sign into their existing accounts with the same credentials as before and purchase content using the same payment methods. As a developer, there’s no change needed to your published products and you can continue to use the same publishing tools to put your app in front of hundreds of millions of Android users. If your app was in Android Market yesterday, it’s in Google Play today.
If you own an Android devices, an OTA update with install Google Play apps instead of the Android Market app on your device. This process will be roll out to users over the next few days. The Android Market app will upgrade to the Play Store app and the Music, Videos, and Books apps will upgrade to Play Music, Play Movies, and Play Books. This update is for devices running Android 2.2 or higher, and users on other devices will continue to have the same access to your apps as before.
The Android Marketplace Google Play can be accessed at http://play.google.com and going to the Android Marketplace website will automatically redirect to Google Play website.