Do apostrophe's matter?

You bet they do.

You might not care a bit about an apostrophe that modify's the word incorrectly, but lot's of people care. They care because it is an instantaneous method for determining whether the person writing is facile with the language and/or cares about doing things correctly.

Now that first impressions are as quick as a few letters in a blog post title (sic!) or a sign in a window, every character matters.