This is great news for developers. Google has updated the popular AppCompat library to version 21, and introduced a new Toolbar widget that will allow for a more Material Design look and feel in apps built for devices running older firmware. This update is exactly what we're all seeing in recent updates for Google Apps like the Play Store or Play Newsstand, and is how we can have the new design language on the majority of Androids, even if they aren't running Lollipop.
If you're an app dev, Google has everything you need to update to the latest AppCompat libs or start from scratch all in one handy reference page. Have a look, and build awesome apps, please.
If you're not a developer, know that these tools mean the people building the apps you love can bring the new look and feel of Material Design to your phone before you get any Lollipop update.
It's great seeing Google build better tools for developers to make better apps. The days of Android apps looking "ugly" should soon come to an end once and for all.