The invitations [from HR at different companies, for second-round interviews] themselves were often a source of much amusement for me as I was subjected to some of the worst English I have read for some time. In one case a spell checker had turned me from a graduate into a gratuity...
I am tempted to mythologize and to say that in the past, the average schmo had a better command of English.
But regardless of how it was in the past, it's definitely pretty bad now.
At a company I used to work at, I didn't compose materials that clients would see; but I told the people who did that I would gladly proofread whatever they wanted me to look at, as I had some skill as a proofreader. While some people gladly accepted (whereupon I caught everything from "in that vain" when "in that vein" was meant, to finding uncountably many cases of "its"/"it's" confusion), the worst offenders continued to assume that their error-thick English was just fine, and that the errors I saw were proof only of my pedantry, and of my desire to just make trouble.
I tried to make it clear that occasionally confusing "their" and "they're" doesn't make you a bad person (and in fact, many very smart people have actual "learning disabilities", to use a loaded term, that make it very hard for them to distinguish such things), but still it does look bad if the wrong form gets into print in a company contract or brochure. Alas, somehow, many people seem to think that "proofreader" is one of those funny old words that doesn't refer to anything anymore, "scullery maid".
At times, I thought: I would not be so annoyed with the HR people if they had actual obvious job skills or knew the difference between "their" and "they're". But the fact that they were feckless and couldn't produce decent written English just made me think that their jobs were some sort of makework for middle-class people who would feel "status-deprived" if they had actually socially useful jobs like waiting tables, or driving busses, or being a clerk at the public library.