PokerStars have created a FAQ (this link works but not if your local DNS server still has the old data) to answer all the concerns for US players. Here are some of the key points:

Regarding player balances:

• You will be allowed to cashout the money from your PokerStars account.
• It will take several weeks before PokerStars will be able to setup a processor to undertake these cashouts.
• No player to player transfers will be allowed involving a US player.
• Any accumulated tourney tickets or tourney dollars (T$) will be converted into cash.
• No ruling yet for FPP Balances.

Regarding future play for US Citizens:

• No player will be allowed to play real money poker from within the United States – even a tourist with an account registered overseas.
• No account registered to the United States can be used to play for real money – even if logging in from overseas.
• Players who can show legitimate residence outside the US will have their accounts reopened and be allowed to play as normal.
• Play money accounts can still be created via PokerStars.net

A summary of these points is that US players should be able to get all their money back, and will not suffer any financial losses, however it will take weeks for this to happen. Furthermore, it seems unlikely at this stage, that we will ever see the return of American players to the major online Poker Rooms.