Sous vide means "under vacuum" and has come to refer to hot water bath cooking, even though it isn't terrible accurate. Many food have the chemical changes we associate with cooking take place below the boiling point of water - this is particularly true of proteins. Getting these right is an essential part of the art of cooking - timing and heat transfer are often critical as you are usually working with temperatures much higher than the important range (quite a bit of meat takes place in the 150° to 170° range for example) at fairly high heat transfer rates.
In water bath cooking (some people prefer that terminology), you put the food in an airtight bag and drop it in a vat of circulating water with precise temperature control - usually to about a tenth of a degree. The food comes to equilibrium with the bath and is cooked for a long time. Sometimes meat are finished over a high heat for a short amount of time to force another type of cooking - generally involving caramelization and the Maillard reaction.
Restaurants, particularly high end establishments, use this technique to ensure uniformity and also to help out with synchronizing dishes - components of some dishes can be done much in advance. A restaurant may have several immersion circulators and there are now specific cooking stations dedicated to the task.
Some amateur chefs get invovled. A few years ago the price of a low end circulator dropped from a few thousand to about $800. Polyscience is the manufacturer - they make a lot of bath temperature control systems for biology, chemistry and medicine.
In the last month Polyscience introduced a lower duty cycle $500 model aimed at the home chef - the Sous Vide Creative. Its pump isn't as powerful, which is probaby a good thing for home use, and the components aren't speced for 24x7 use - otherwise it appears to be the same thing as the $800 Chef series. William Sonoma distributes both of them and also features vacuum bagging machines
The market for $800 machines has not been great - what may have pushed the home Polyscience unit is a Kickstarter project from Nomiku. It turns out dedicated amateurs have been building their own machines - but a lot of these have been piano wire and chewing gum. The Nomiku will be even less expensive at about $360. That is starting to get attractive. The Nomiku has a stronger pump than the Polyscience, but only has 750 watt heater as opposed to 1100 watts. I'd like to see how these compare in the wild - but the Nomiku is new with deliveries starting in a couple of months. If it works well the Nomiku looks particularly attractive for home use. I shouldn't even require a lot of counter space. Also note the use of simple ziplocks ... not optimal, but probably good enough for many purposes.
If these become popular it may be that we'll see sub $200 units. That would get a lot of people interested. I'd probably get one. But if someone wants to fund a Polyscience for me now, I won't complain... I'd happily take a Nomiku too....