WidgetLocker 2.0 is a major update and adds many new features, optimizations and bug fixes. However if you try 2.0 and for whatever reason wish to go back to 1.2, I want to tell you that you can.
WidgetLocker 2.0 changes a few internal formats which means if you just try to run WidgetLocker 1.2.8.1 (The last Market release before 2.0) it will likely force close. To work around this, I’m providing WidgetLocker 1.2.9. WidgetLocker 1.2.9 is compatible with WidgetLocker 2.0 style internal formats, but contains no other significant changes since 1.2.8.1. This means if 2.0 introduced a new bug, or removed a feature you miss, you can safely downgrade to WidgetLocker 1.2.9 and use that until 2.0.1 or 2.1 or whatever version suites your needs.
Note, this APK requires you have legally purchased WidgetLocker from the Android Market.