From the way the release is worded, specifically this part:
XNA Game Studio 3.1 is here!:
- Visual Studio Changes: XNA Game Studio 3.1 supports both 3.0
and 3.1 projects, and it includes support for upgrading projects from
3.0 to 3.1.
Submitting 3.1 Games
XNA Game Studio 3.1 games can be submitted to Xbox LIVE Community Games starting late July.
Please note!
Currently, if Premium Creators want to submit or service their game
to Playtest and/or Peer Review, those games must remain XNA Game Studio
3.0 projects. On July 23rd, you can submit games upgraded or created as
3.1 projects to playtest and/or Peer Review, but they will not go live
to consumers until we are able to upgrade Xbox LIVE Community Games
Marketplace later this Summer.
It sounds like you can still submit 3.0 games. I hope so, since I have one that's very close to release. :-)
[edit]: I guess Nick's link sums it up even better!
"Software is never finished, it is in varying states of 'less broken'" because "If it ain't broke, it doesn't have enough features yet"
The signature that was too big for the 512 char limit