One thing that really bugs me is how anal many people are about the English language. Last year I had to deal with a case at work where someone told us that he couldn't find a word we were using in his dictionary, and told us we therefore should not be using it, in spite of the fact that it had not been coined by us, but by the industry regulator! I've encountered this kind of petty, small-minded attitude too many times, and it drives me up the wall.
People like that seem to think they're the self-appointed guardians of the Queen's English (that probably covers the entire of the Commonwealth as well as the UK, don't know what people in the US would interpret as being correct English in the same way - any suggestions?) and that they're single-handedly preventing the language from sliding into the gutter. Usually scared by endless Daily Mail articles (along the lines of "Children using text speak in schoolwork/exams! End of civilisation imminent!"), these people seem to think that the way people speak or write is an affront to the whole English language. I find this sort of attitude incredibly stupid and ignorant.
Thinking that something is not English because it's not in the dictionary is putting the cart before the horse. The English language predates dictionaries by many centuries, although naturally it has mutated over its lifetime. Although there were other dictionaries beforehand, the first really popular and reliable dictionary was A Dictionary of the English Language by Samuel Johnson, published in 1755. Until dictionaries became popular, words generally had no fixed spelling.
A dictionary is not a definition of the English language, as some people seem to think. It's actually a record of the English language as generally spoken at a specific point in time. The Oxford English Dictionary styles itself as "The definitive record of the English language". A word does not come about by being added to the dictionary (otherwise the publishers of the OED would have to invent them - "Hey, what word shall we invent today? Snungfurbdle? It's going in!"), but by passing into common usage. Once a word is commonplace enough it may be included in the dictionary, but the dictionaries are not the arbiters of what the English language is by choosing what words to include, any more than newspapers are the arbiters of what is going on in the world by choosing whether or not to report it. If a dictionary does not include a number of words that many people use, it does not mean those people are in any way mistreating the English language, it means that by not having a record of those words the dictionary does not paint an accurate picture of the language in its present state and is thus deficient.
Furthermore, many technical terms will never be used by the great majority of people and thus will never gain sufficient currency to be worthy of consideration for inclusion in a dictionary. That doesn't make these terms wrong, they're just not in common enough usage to be worth including.
English is a highly fluid, flexible and ever-changing language, and in practical terms it's almost impossible to pin it down. It's spoken as a first or second language in the UK, US, Canada, Australia, New Zealand, South Africa, India, Pakistan, Kenya, and many other places the world over. With so many different speakers with different dialects constantly influencing each other, and a fast-moving world where new terms are being coined all the time, and others being imported from other languages, then in practical terms it's unreasonable to expect the language to remain static. If you don't like it, tough!