The Waterpik is technically called an "oral irrigator." The idea is to use a pulsating jet of water to clean tooth surfaces and between teeth.
The Waterpik has been around since the 1960s, and pretty much just stayed around, without growing very much or going out of business.
In an effort to link itself to the growing interest in dental floss, the Waterpik is now calling itself the "Water Flosser." Some people are referring to this as "Power Flossing."
The company has done studies to compare the Waterpik to flossing and it seems to work, to some extent, but no one but the company is saying it can be used instead of flossing.
Water flossing may be handy for people with braces, and some people may really prefer it to flossing.
It's surprising though that the company's "Patient Education Video" on the newly renamed "Water Flosser" contains a pretty young woman smiling and using the product while dribbling so profusely. Check the video and see if you find it a great education or sales tool.
http://www.waterpik.com/oral-health/videos.html?id=6
One of their other videos "Stop Looking at Your Leftovers" shows a smiley young guy flossing and popping food pieces on his mirror. Later when he uses a Waterpik, he doesn't dribble on camera. The funny thing about this is how messy a Waterpik can be when water gets out of your mouth and starts squirting around the room. If you look at the "Clinical Studies" listed on the website you can see that Waterpiks were more effective at cleaning the facial surfaces (front) of teeth and less effective on the lingual surfaces (back of teeth, where your tongue is). When you turn a Waterpik to face the back of your teeth, it usually splashes water out of your mouth, which probably discourages people from cleaning back there. And you dribble.
Floss on!