It looks like the first AT&T Android phone, the Motorola Backflip, will have Yahoo! as the default search engine, and not Google.  A bit odd.

Then, it sounds like AT&T is not allowing Backflip users to install non-market apps for Android:

http://www.engadget.com/2010/03/08/motorola-backflip-doesnt-allow-non-market-apps-proves-atandt-doe/

http://gizmodo.com/5488495/att-doesnt-allow-non+market-apps-on-android+based-motorola-backflip

Also, it appears that T-Mobile is the one who has embraced Android more than AT&T with their decision to ditch Yahoo! and use Google as their default search engine on their devices:

http://www.phonescoop.com/news/item.php?n=5608

What does this mean?  Not sure, but it seems to me that AT&T is not totally embracing Android at first.  So, it will be interesting to see what the HTC Android phones are going to be able to do when they come out.