I've worked in several libraries which use the Library of Congress classification scheme, and on the whole I get on well with it. It's a scheme usually found in university or other large libraries. At the moment I am having a crash revision course in LC classification as we are planning to reclassify a section of our library which has hitherto had its own idiosyncratic in-house scheme. The in-house scheme is simpler, but as is the way with such things it does not cope very well with changes of direction in subjects (larger schemes such as LC or Dewey have more flexibility built into them).
I've used LC in every large library I have worked at, and used it as a library user too, so I have been quite surprised to find that libraries using it seem to be in the minority. This is frustrating my attempts to cheat by lifting other people's numbers - and I am also finding that all the libraries who do use it seem to break down at some point and start introducing their own variations. Even the Library of Congress itself can be inconsistent in how it applies its own classification scheme.
At the moment my main source of LC-inspired distress relates to its shaky grasp of British geography (and law). Of course it is an American scheme, and as such is Americentric. The order in which countries come tends to follow a pattern which puts the Americas first whenever a section is divided geographically, followed by Europe. This is absolutely fine, although I find it a bit strange that the main history sections don't follow the same pattern (Europe comes first there, with America trailing far behind).
Slightly more vexing but still understandable is the fact that some sections go into great detail for the Americas, particularly the US, but then throw in one number for "other regions and countries" which seems to mean "the whole of the rest of the world". Of course the scheme was meant for the Library of Congress's own collections, but at this point it becomes a lot less useful for everyone else. We are trying to get away from having shelves and shelves all at the same number, which is what following the scheme to the letter would produce where dealing with a collection which is mainly about other regions and countries. Here begins the slide down the path of local variations, which can seem like a good solution at the time but bring their own problems in the future. (Dimly I am now remembering being told in a previous job to use all the lovely detailed US numbers for Britain. OK, but then what happens when you get books which really are about the US? Does it become one of the "other regions and countries"?)
More of a problem than the emphasis (which is expected) is the sheer uncertainty with which the Library of Congress, both in its classification scheme and in its subject headings, contemplates British geography. On the one hand, until fairly recently it didn't really seem to understand the distinct nature of the home nations at all, but at the same time it also did not (and still does not) acknowledge the United Kingdom as an entity. This is perplexing to British users, who usually encounter either those who care about the Union and wish the United Kingdom to remain united, OR those who are quite clear about its separate parts having separate identity (and it's possible to do both - but not usual to do neither). The Act of Union predates the Library of Congress (and predates American independence, come to that) so why does the UK have no place in its scheme? On the other hand, despite the Act of Union, Scotland has always had its own separate legal system, so what is this "Great Britain" which pops up everywhere in inappropriate places?
On a more local level, Monmouthshire is still in England according to the classification scheme (along with all its towns), although the subject headings have caught up and put it in Wales. The Isle of Man seems to be treated as an English island (don't tell them!). I am generally in favour of standards for the sake of consistency over the years (we have too many examples in our use of the scheme of strange local practices the reasons for which have long been forgotten), but I am going to have to make some exceptions for some of these.
I realise I may be a bit of a pedant. On the other hand, if devising a system of organising knowledge, at least try to avoid inaccuracy!
Here's my rough guide to Britain and British mysteries, especially for our friends at the Library of Congress (and others who may be perplexed):
The British Isles: geographical term referring to all the islands. No politics involved.
The Channel Islands: British crown dependencies. Not England. Not UK. Not really part of the British Isles but near enough ...
England: the biggest bit of the main British island. East of Wales and south of Scotland, no overlap!
England and Wales: a legal jurisdiction. (which Great Britain is not. Despite the subject headings.).
Great Britain: the biggest island in the archipelago. (Also known on the Isle of Wight as the North Island).
Ireland: second largest island in the archipelago. Split into two territories due to partition in 1920. The Republic is an independent state.
Isle of Man: island in the Irish Sea. Another crown dependency with its own parliament. Not part of the UK! Definitely not part of England and never has been!
Isle of Wight: island off the south coast of England. This one really is part of England!
Monmouthshire: is in Wales. Always has been, although its position was ambiguous particularly in the 19th century.
Northern Ireland: the official name of the part of Ireland which remains part of the United Kingdom. It is not in Great Britain though: there is a sea to get across!
Scotland: the northern part of the main British island, with islands of its own. A Kingdom (same monarch as England since 1603); united politically with England by Act of Union 1707. Has always had its own legal system & education system (and now has own parliament). Is a legal jurisdiction (which Great Britain is not, see above!)
Tynwald: the parliament of the Isle of Man, supposedly the oldest in the world. The House of Commons is an upstart in comparison!
The United Kingdom (= of Great Britain and Northern Ireland) A legal jurisdiction! Includes England, Scotland, Wales, Northern Ireland. The government elected to sit in Westminster is the United Kingdom government. Not the government of Great Britain (which is a large island but is not a legal jurisdiction, yes?)
Wales: Is not part of England. Henry VIII's Acts of Union in 1536 and 1542 absorbed it into the English legal system (hence "England and Wales"). Is part of the main island, also has some islands of its own. Now has some devolved powers and an elected Assembly.
All quite simple really! (I'll leave Cornwall for another day ...)