This is a smart move and it will likely pass.
Most Greeks hate the bailout deal, but the vast majority want to retain Euro membership. This pretty much forces the Greeks to put up or shut up and if the referendum passes, it will make it clear that the union mobs on the street are very loud yet lack much influence.
And if by some chance it fails, that is a good result in the long run as well. Greece will default, go back to their currency and be forced to actually live within their means.
The referendum is a good idea, though I expect the other European countries to try to force Greece to cancel it. The EU doesn’t actually like democracy, and when a population doesn’t vote the way they want they will insist on re-votes till the people “get it right”.
Could be the only way for Papandreou to get through to the pig headed Greeks what’s really at stake for them here.