Interesting numbers. I think it can mean this attacker can do a few things:

They can generate way more than 50 BTC per block. But then the 'normal' clients will ignore the block chain generated by the attacker as the blocks don't follow the rules. This may be an annoying attack, but the 'normal' blockchain would still be generated in the background as normal.

The wiki https://en.bitcoin.it/wiki/Weaknesses lists some things that he can do while following the rules: (section "Attacker has a lot of computing power")

• Reverse transactions that he sends while he's in control
• Prevent some or all transactions from gaining any confirmations
• Prevent some or all other generators from getting any generations

Maybe someone else can elaborate on how much impact these things have, in the short and long term.