In here, we shall gather to report to one another the errors in grammar and spelling of those down upon whom we look. Be as snooty as you like. Pick nits. But be kind. Remember that they are not as erudite as we.
From the BBQ Pit, a dangling modifier: Arab militia decapitate American with knife
Got a problem with commas there, Lib? 
Not really grammar, but more pronunciation.
The T in the word, “often” is SILENT!
Actually, what I hate more than any grammatical error, is the quickness to call someone a “Nazi” because they offer mild and constructive criticism.
I nominate the inability to distinguish between **its ** (the third person singular neuter possessive adjective and personal pronoun, possessive case) and **it’s ** (the contracted form of *it is * or it has). This is a common grammatical error in many English-speaking countries. It’s particularly prevalent here in Australia.
I’m going to bring up my pet peeve yet again. People who continually confuse then and than.
To me, it seems to be far more prevalent than the ever popular their/there and your/you’re confusion.
From IMHO:
What’s the best cheap, car to possibly get my brother in law through school?
One hardly knows where to begin.
I remember this being discussed in a previous thread, and looked it up (from dictionary.com):
I would be honored to be one of those down upon whom you look.
In a recent pet naming thread I misspelled my own dog’s name. Missey instead of Missy.
Will you add me to your list?
It would make my week to see or hear anyone in real life (as opposed to on this board) use lay/lie correctly. Sometimes I think if I hear one more person say something about “it just laying there,” I’m going to ask them for the eggs!
I may not be the Poster Girl for Grammar, but I do try my best. Please feel free to ridicule me for any grammatical errors that show up in my other complaints.
Homophones and people who have never learned to use them–that’s what drives me nuts. Too, to. There, they’re, their. The aforementioned its and it’s.
And I would appreciate a nationwide seminar on how to spell separate. I don’t know why that one mispelling bothers me so much.
Then there’s the delightful confusion of infer for imply.
The speaker implies; the listener infers, folks. Imply is to, infer is from.
Thank you, I feel much better now… 
I don’t know who to tattle on, but there’s no such word as definately as far as Merriam-Webster or I can tell.
Discreet/discrete, anyone?
Discreet: showing discernment or good judgement
Discrete: individually distinct
And may I discreetly point out that most of us are not picking on thread titles as we were told to do?
PC Load Letter: what does it mean?
Shouldn’t W be capital after a colon ?
ANY loose/lose confusion.
“I hope I don’t loose too much money at the casino.”
“These pants are really lose.”
ARRRGHHH!!!
Thank you, I feel better now.
Actually, now that I think about it, I’m not sure it’s really a grammatical error either. But if you’ll excuse the possible hijack, I’ve run across two examples of this mistake in two days and I’m gnashing my teeth over both of them:
“More and more dictionaries were being published, each one bigger than the next.” (slight paraphrase, from The Professor and the Madman). Sorry, but I believe you’ve just said the exact opposite of what you very clearly mean. (Trust me, it’s clear from the context.) Each new dictionary was bigger than the last.
“The importance of taking Communion in Catholicism cannot be understated.” (heard on All Things Considered today). Once again, what you actually meant to say was that its importance cannot be overstated.
C’mon, people, use your heads!
Or misspelling, even… 
But I agree that people who think the word is seperate aren’t quite up to par.
Here are my nominations* – the all-too-frequent misuse of “reigns” and “compliment”. A coach may metaphorically reign over his players, but he does so after taking the reins of the program. Meanwhile, players on the squad may well compliment each other by saying nice things. If their varying individual abilities mesh, however, those discrete skills complement each other.
*admittedly not taken from specific SDMB threads, but I’m sure a search could eventually turn up several examples of both
Dangling modifiers are hilarious. Zucker Abrams Zucker used these effectively in “Airplane” and the TV show “Police Squad”
Ed: We found the ransom note. We sent it to the lab. They want a million dollars.
Frank: Why does the lab want a million dollars?
Okay, now for my grammar gripe. Not really grammar per se, but over the past 10 years or so, when did we stop using the past tense when we’re talking about events in the past?
Example: Last week I’m in a car accident and I see the other driver is really angry. Before he gets out of his car, I’m calling the police on my cell phone…etc
Any other SDMB folks notice this “trend” is getting very prevalent ?
Sorry for not sticking to the OP.
Well here’s an ambiguous thread title right here in MPSIMS:
“Disturbing Church Marque Message”
I guess that thread concerns vandalizing church signs?