Waitrose is one of the big supermarket chains in Britain, formed in 1904 by Wallace Waite, Arthur Rose and David Taylor. It is currently owned by the John Lewis partnership (which took over control in 1937), which all employees own shares in; effectively, the employees own the company (handily stopping the company from being bought out). Their current market share is currently around 3%, due to a number of factors (they are commonly known as a very upmarket and expensive store, a stereotype which isn't completely wrong). The first Waitrose supermarket was opened in 1955 (after the Lewis buyout) in Streatham in London.
Waitrose caters to the same upper-middle class demographic as Marks and Spencers. Their slogan is "Good food, honestly priced", which is a frankly fantastic way to cover up the fact that practically everything in there is ludicrously expensive. They sell some pretty damn good stuff (for own brand items, at least), but doing weekly shops at Waitrose is limited to those willing and able to blow their noses on ten pound notes. That said, when Waitrose cut prices they cut them hard (example: I picked up some kind of fancy bread recently which was cut to £0.15 from £2.79, although that might have been due to that recent Christmas business).
WR currently have 173 stores nationwide and are looking to expand (two more stores are due to open soon). They recently purchased some 17 stores from Morrison's, who were obliged to sell off certain ex-Safeway stores as a conditon of their buyout of the aforementioned chain). The goal is to have 230 stores in the UK, and they do not currently have any stores abroad (nor, it would seem, any plans to have any, especially after M&S's recent hijinks in mainland Europe).
They have an online shopping service, bizarrely named Ocado for no clear reason, 46% of which is owned by the Lewis Partnership. Unlike most other UK online food shops, Ocado uses warehouses rather than local stores, completely bypassing all the finicky business of "does my local store have this exact variety of x which I require and for which no substitute is adequate".
Advertising tends to be based on waxing lyrical about how exotic their products are or how pointlessly complicated their production processes are, along the lines of "Only one chain sells beef that was beaten to death with the bodies of ancient dodos, floated down the River Nile for 100 miles on a small raft made of cedar wood, thrown out of a third story window into a bucket of liquid gold and then used in some form of bizarre circus" (well, maybe not that pointlessly complicated, but you get the picture). The "honestly priced" bit comes into play when a description of the product and its price/price per kilogram (usually in the realm of around twice its less-travelled equivalent in the Sainsbury's across the road) comes on screen. This is as opposed to the recent "food porn" approach of Marks and Spencer, where they flash lots and lots of delicious looking food at you and extol just how amazing it is, completely failing to tell you the price. Bastards. (But I digress...)
In terms of business practises, Waitrose comes nowhere near the unsavouriness of certain other chains, especially with regards to supplier relations. A government report stated them as having requested payments from suppliers as a condition for stocking their products (and additionally for better store placement). They were however a member of a small minority of chains which did not threaten to delist suppliers unless they reduced prices (delisting is the act of discontinuing supply from a particular supplier, sometimes leading to bankruptcy on the part of the supplier). All in all they can either be seen as the best of a bad bunch or the most ethically sound supermarket chain, depending on your viewpoint of course.
Update (July 2006):
Wikipedia article as of 26th Dec 2005
Joanna Blythman; "SHOPPED: The Shocking Power Of British Supermarkets", ISBN 0-00-715804-1
I'm now officially a Waitrose employee, and have been since May. w00t