Depending on the time you want to take, and the quality that you require there are many ways to extract an image with fine edges.
In the image below, I created a duplicate layer of the girl above the bubbles background. The top layer of the girl is set to Multiply around 80%, the layer beneath is Normal 100%. With a fuzzy round erase brush (in this case about 30 px) at 100%, I erased the second image (normal layer) around her head and over the floating strands (anything that was just outside the fullness of her hair). With a smaller brush, I erased around her face & hand. This preserves the hair and gives it a bit of the background color similar to what you'd normally see. It takes more selection when taking the model out of a complicated background, but works well on white.
http://http://www.artofthegroove.com/images/other/background_2.jpg