I quite like the use of dialect in a novel, though of course this doesn't mean it's bad English. Irvine Welsh, Niall Griffiths and James Kelman do this brilliantly. It can be quite hard to read at first, but I try to think of the characters speaking in that accent and it works.
My idiot gets all sorts of things wrong and I had fun with getting a Polish girl correcting his inept English.
Oh yes. I like dialect in novels although it can be difficult to read as you say. I love the idea of a Polish woman correcting!