Usually, the winner in a presidential election, particularly if it is a solid victory, gets a big boost in legislative elections (which polls showed Sarkozy getting) so this is an important victory. French voters, who elected Sarkozy largely on a "law and order" and anti-immigration platform rather than his anti-labor, anti-welfare state proposals(which the press here has emphasized) have sent him a message that they don't want their work week extended and their effective national health care system undermined. While the president of France has great powers under the Fifth Republic (greater formal powers than the U.S. president) Sarkozy hopefully will get the message.
The Socialists should also get the message and use their strengthened position in the legislature to actively defend workers rights against the Sarkozy government. The Communist Party's loss of seats was especially unfortunate, not only for the party, but much more for the French working class. A strong vote for the Communist Party, capitalists everywhere understand, is the most powerful message workers can send in an election any capitalist country to the ruling class that they will not accept concessions and givebacks on the gains that they have made.