National Grammar Day:

Arnold Zwicky (Language Log) has many wise thoughts on the subject. Here's one, though you should read the whole post:

[T]he assumption that non-standard variants are unclear and therefore impede communication ... is mostly just taken for granted, without any kind of defense -- in what way is "between you and I" less clear than "between you and me"? in what way is "all shook up" less clear than "all shaken up"? they're non-standard, certainly, but LESS CLEAR? -- and the occasional explanations of how particular non-standard usages are unclear don't survive scrutiny. Instead, it's just an article of faith that non-standard variants (and conversational, informal, and innovative variants, and variants restricted to certain geographic regions or social groups) are unclear, vague, sloppy, or lazy ....
This has been my experience as well, not in all instances, of course, but in many: Often people complain about some (supposedly) novel usage, and assert that it's stripping the language of clarity or precision or useful distinctions, but on closer analysis the assertion proves to be unfounded.