I could make this post very long, but instead I will give the short and sweet version.
(I am generalizating somewhat from my case to the mostly likely affected scenario.)
If you want to play a mov video file that uses an mp3 codec (such as the video files in the Dimensions video series) on your Android 2.2 based phone, the audio does not work when using the default video player. I (more-or-less) submitted a bug report to Motorloa about this, so hopefully future versions will work correctly. In the meantime, the (free) arcMedia app plays the video correctly.
In addition to actually supporting some audio and video codecs that Android is supposed to, arcMedia also supports many other formats that Android does not, such at wma and wmv.
This is the kind of functionality that I expect from VLC Player, which is not in the Android market yet.
To download arcMedia on your Android phone, scan or click the following QR code: