I'm surprised that no-one seems to have noded this before... this will be a far-from-comprehensive w/u, but the show deserves something...
Coronation Street is the UK's longest-running TV soap opera (The Archers on Radio 4 has run for longer) and one of its consistently highest-rated shows. 42 years from its creation the show is stil so successful that questions were actually asked in parliament when Deirdre Langton-Barlow-Rachid was jailed in the show, and Prince Charles even made a brief guest appearance for the 40th anniversary show (his voice only, heard on a radio in the show).
Created by Tony Warren in 1960, Coronation Street was originally set to run for 13 episodes (with a proposed 14th episode where the street would get bulldozed) , but was so popular that it is still running 42 years later.
Originally the show was a 'kitchen-sink drama' of the type that predominated in British TV and films in the late 50s and early 60s, but over the years the show developed a strong comic element, and many of its most-loved characters have been 'comic relief' characters such as Hilda Ogden, Reg Holdsworth, Fred Elliot and Roy Cropper.
Set in the fictional Manchester area of Weatherfield (from the occasional clues given in the show, this appears unsurprisingly to be in North Manchester somewhere near Granada's Deansgate studios, with location filming mainly taking place in Manchester city centre and in Salford), the show was originally based solely around the street of the title (supposedly built in 1952, hence the name) but over the years various long-running characters have moved to nearby areas in Weatherfield, although the main action usually takes place in the street.
The action, other than that which takes place in the characters' homes, takes place in three main areas:
The corner shop, which used to be run by Alf Roberts (also a local councillor), and later by Reg Holdsworth (one of the show's comic relief characters, known for his ridiculous glasses).
The Kabin, a newsagents run by Rita Sullivan (one of the principal problems in the show is to make this look like a fully stocked newsagents while at the same time not stocking any magazines featuring the show's stars on the cover).
And most famously the local pub, the Rover's Return. This is probably the most famous part of the show, and has spawned some of the most famous characters, such as former landladies Bet Gilroy and Annie Walker and barmaids Racquel Watts and Betty Turpin. Almost all the action, such as it is, in the show has taken place here, including at least one death.
Currently shown 4 nights a week on ITV, the show is apparently in a minor slump quality-wise (I haven't watched it in a while), but overall maintains a remarkably high consistency for a show of its type. The fact that the show also has a lighter tone than its rivals Brookside and EastEnders also means that when it tries to deal with 'issues' it does so far more successfully than the other shows. For example the other soaps have made the occasional attempts to introduce gay characters, but these characters are almost exclusively defined by their homosexuality and are usually written out fairly quickly. Coronation Street on the other hand has had for the last 4 years a regular character who is transgendered (Hayley Cropper, played by the non-transsexual Julie Hesmondhalgh), yet mention is rarely made of this fact, and she is just another woman in the majority of storylines, in a stable relationship with her husband Roy, and one of the most sympathetic and realistic characters in the show.
Obviously over the years a show that has run as regularly as the Street has had a huge number of regular characters. Some of the more noteable characters I haven't mentioned include Jack Duckworth, Vera Duckworth, Mavis Riley, Elsie Tanner, Mike Baldwin, Alec Gilroy and Stan Ogden. But special mention must be made of Ken Barlow (played by the William Roach), who has been a regular character for the entire run of the series since episode 1, despite the fact that he is probably the least interesting character ever to appear in the series, and Roach may be the worst actor in the cast (the quality of performance in the show is remarkably high for a programme that has such a fast turnaround of episodes). Barlow's feud with Mike Baldwin (and their frequent marriages/affairs with each others' wives) over the last 20 years or so has provided many of the longest-running plot strands, yet I honestly believe that if the character were written out tomorrow few if any people would notice.
SharQ has pointed out as well that there is a Coronation Street website at http://www.corrie.net