If you can get your hands on "Blooming English" by Kate Burridge, it's a fascinating read. Prof. Burridge is an Australian linguist, but she's not prejudiced at all and in her book makes frequent references to other varieties of English. In "Blooming English" she writes about the evolution of English, but it's not a dry historical linguistic account of the changes English has gone through, but a lively current description of the changes English is going through right now.
Just to give a taste of it: bought or brought? Apparently, "bought" is slowly taking place of a past participle "brought" and usage such as "I've bought this book back and would like to exchange it for a different one" is becoming more and more common. Mind you, it will be many many years (think centuries) before the complete change will come about (if at all), so for now, stick to "brought", but don't be surprised and do not necessarily consider it a grave error if you see or hear "bought" rather than "brought".
And one more: ain't and singular "they". Those of you who have a strong aversion to "ain't" and singular "they" (and themself) - take it easy. Both "ain't" and singular "they" have a long tradition in English. While "ain't" has fallen from grace, singular "they" makes perfect sense and looks much better than the akward "he or she" or the ideological "he".
"Blooming English" was first published in 2002 by ABC Books and in 2004 by
Cambridge University Press.
Happy reading!