Not quite a grammar gaffe, but along the same lines.
My eldest daughter has just started high school and I am very interested in her school work / homework.
I was looking through one of her maths books the other night, just checking to see whether I could remember any of it - amazing how quickly it comes back, even simple things like prime factors, etc.
Anyway, I use figures in my typing at work (invoices, etc.) and if I have to use "thousands" I use a comma to break up the thousands, i.e.
£10,000.00
In my daughter's book (correct use of apostrophe(?) as the book belong to my daughter), it says that in the "old days" thousands used to be separated by a comma but now it is common practice to just use a space, i.e.
£10 000.00
Did that make me feel old.
I might get shouted down here, but I feel that grammar and spelling are two of the things that "younger" people are no longer interested in. The way my DD (nearly 12) writes e-mails, she uses shortened words like she does when she texts on her phone - but I can't even think of an example because whether I am e-mailing, typing a proper letter or texting on my phone, I never use shortened versions for words. So someones e-mail/text message would be 2 lines long and mine ends up being about 20 lines long but I just can't shorten words (although obviously I can "proper words" like can't, wouldn't (as I have used in this message).