What is always rather lovely is that the people who go crashing onto a thread just to point out an error always, without exception, make far more glaring ones themselves. Always. I do a bit of community service and point them out publicly if someone is being a total cunt about it, but y'know, not being a sad fuck who gets my rocks off by belittling others I try and be the better person.
I suppose we should be magnanimous and think that their little lives must be so devoid of praise and self-worth that they somehow feel better about themselves having pointed out that it's not "should of". (Have you noticed how they always think they're the first person on Planet Earth to have spotted it as well, bless)
There are some people on MN who write beautifully, succinctly, and with enormous wit. Strangely, you never see them putting other people's use of English down. Whilst the people who do it, and do it regularly, have a command of English which generally seems to be adequate at best, and somewhat mediocre at worst.
The "oooh, it's getting like Nethuns" comments aren't necessary either. Although possibly true, in that I believe Netmums has a reputation for bullying mean girlz pulling pigtails in the playground, which is, after all, what the Grammar Police are doing.