I've held onto stocks that I think will eventually do OK...sometimes the losses for me have been over $1M on some that I think will go back up at some point... you have to ask yourself these questions:
Are you willing to absorb the commission to buy and sell the same stock back if you sell?
How long are you willing to give a stock before dumping it? $1 loss? 2? $5?
Personally, I tend to ride out the swings on stocks I know will come back.. for example... when James Cameron announced he's having writing issues with 2 major stocks, it dropped today 14+ points, but I didn't sell... I lost over $3M in 1 day on those two, but I couldn't log in due to work to stop the bleeding, so I'll just hold onto them and figure that they'll come back... but I also have the cash to be able to do that...not everyone does.
It all depends on your tolerance for how much of a loss you can take. Sometimes I sell off the 'slow bleeders' - the stocks that drop 25 cents here, 10 cents there, etc.
Good trading!