My vote goes to people using "it's" for "its". Another that makes my skin crawl is "would of", "should of", etc. Or making plurals into singular possessives, such as "we are buying some book's today". Or not knowing the difference between "affect" and "effect" or "then" and "than".

The end is nigh. In hard copy, the Nanaimo Daily News is the worst newspaper I've ever read in terms of missing words, typos and grammatical errors. However, the Vancouver Sun (not to be confused with the Toronto Sun chain of rags), has had a number of errors the few times I've picked one up.