Just really puzzling. The problem seems rather obvious based on the take-away polling question [emphasis added]:

Based on what you know or have read about the new Arizona immigration law, do you favor or oppose it?

Really? Gallup polled adults nationally about a law that only applies to one state and that, at the time of the survey, had only really been in the national news for a few days, and assumed people who had “heard” of the new law knew what the law was about? That strikes me as odd.

But it's true:

Note that the poll did not attempt to measure actual knowledge about the law or describe the various provisions of the law to respondents.

In the write-up of its findings, Gallup explains what the Arizona law means:

The law makes it a state crime for illegal immigrants to be in the country, and allows Arizona law enforcement officials to detain those suspected of being in the country illegally unless they can prove otherwise.

You could definitely quibble with that characterization as being overly gentle. But wouldn't it have made sense to read something to polling respondents in terms of explaining the law and then ask them if they favor or oppose the law, rather than asking them that question without having the slightest idea if respondents understood what the brand new, Arizona-only law meant?

UPDATED: NBC's Chuck Todd tweets that the Gallup poll is “VERY misleading”