First off, I'm really excited about XNA/etc. If I ever meet the guy/gal who came up with this idea I would love to buy them a beer.
I'm a programmer with professional experience. I feel like I'll be comfortable with XNA development once I've got my hands on it. My main concern is game assets. I'm no artist, nor am I a sound engineer.
Here are my questions:
How much art/sound content is expected to be available for programmers like me
Will there be a variety of content For example, I want to make a fantasy RPG and some other guy wants to make a space themed FPS. Will we both have access to the assets we need
Will art and sound types be able to upload their own content for other developers to use

Art/Sound assets
Warren13
Boy I wish I found this earlier.
Pintoo Khaira
Max Damage Studios will be releasing game sound packs for free community use.
http://www.maxdamage.net
We'll also have music and take custom sound requests for a very small fee. The packs will probably be released in early December, just before the full version of Game Studio Express. I know exactly how much "stuff" you need for a successful game (it's not just code), so we're looking forward to contributing to the community.
Spooner
Bookmarking that site now. Thanks!
The Missile Command game looks pretty cool.
CodeSweatAndBeers
Maybe there are others out there like us who are really into the programming but can't draw worth a damn. Anybody want to point us in the right direction for some free/PD game art assets like sprites, backgrounds, textures, meshes, etc
Chaseman
Great to hear your enthusiasm.
For the first version, the starter kits XNA will be providing (from a variety of genres) will probably be your best initial source for assets. Beyond that, a longer term goal is for an XNA community where assets will be able to be easily shared.
Amy
godsarmy
http://www.texturebin.com/
I found this resource thanks to reading a tutorial on this site http://www.xnaresources.com
Colin Reid
http://forums.indiegamer.com/showthread.php t=8409
Also a very good forum if you're an indie or thinking about going indie. I've been a lurker there for years now.