As someone who has worked in proof-reading and copy-taking, as well as a correspondence department, it is amazing how many spelling mistakes make in to professional works nowadays. Literature from companies like Sony, Panasonic etc (although in a lot of cases with them it is a translation error which is always amusing), most of the newspapers are now quite horrific in respect of their printed werd. Magazines like What Hi-Fi have also become more amusing to read for the errors than the articles (which are almost errors in their own right sometimes!......love that £50 USB cable...hahaha)
Most of the time, the errors are as above, you instead of your, an instead of and etc. But an increasing number of less understandable errors too, grammatic as well as spelling. With magazines/papers, I could at least be willing to consider that sentences missing a word are simply because the article would be too long, so they are taking the lazy way out of managing this, but with articles on the interaweb, or if there is plenty of space on the page in a mag/paper......
Spellchecker would normally pick up a word missing from a sentence as the sentence wont make grammatical sense in most of those cases without it. I honestly think people have moved from being lazy enough to need one, to being apathetic (or egotistical) enough not to bother using it.
ps. please dont bother picking out any mistakes in my post, its first thing in the morning, I've been worked like a dockside woman-of-the-night for the last few days and my arthritis is killing me, so there probably are some and I couldn't give a monkeys