I don't believe the War Powers Act has been violated. Supporting NATO actions is something within the President's discretion as commander-in-chief. No troops or units have been committed (unless I missed that post or article), only air force has been sanctioned, and Congress notified of air missions. That being said, I do not agree with the President's decision -- it seems impractical to be engaged in a long uncommitted standoff with Libya.
It seems politics are getting in the way of common sense here. If the President, arguably justified or unjustified, commits troops to a US operation in Libya, he will have to deal with the political unpopularity as the Republicans gear up for their primary, allowing them to look like peace-loving pacifists for the first time in decades. If the President simply stops providing support to Libya at this critical juncture, it would be both irresponsible in the short and long term -- the effects in the short term on Libya, and in the long term, of what the Middle East region thinks it can do to get by the US in the future.
To be honest, I thought the situation would be handled shortly after OBL was killed, but for one reason or another, we seem reluctant to get our hands dirty against an estranged dictator, sovereign or not.