The Appbrain app is offering to update my Maps, Street View and Facebook app. In the Android Marketplace, I can't see any option to update (though I have never updated an app before so I don't know how the update would appear). I am wondering if this difference has something to do with HTC customisations. Should I allow Appbrain to update these applications or not?
Were these pre-installed apps? You won't get market update notificatins for apps that are pre-installed, you have to go to the market and manually install any newer versions of the app and then you'll get future updates via the market.
The same thing happened with my Droid. I heard about an update for Facebook (which came on my phone), but never saw an update in the market until I searched for it and manually installed the app.