"With the next Android release, Google could get around to fixing its app Market's weaknesses—and maybe you'll get that update this year. In the meantime, AppBrain does a spectacular job of making apps easier to search, install, share, and manage.
Why bother with a third-party app manager? Because AppBrain primarily provides a better three-step app experience—Search, Install, Update—for Android apps than the default Market, especially on phones that aren't caught up to the Android 2.2 experience."