A list of common English mistakes often seen at BGG, including many related specifically to gaming, e.g.: cavalry/Calvary, die/dice, lose/loose, rogue/rouge, role/roll, ... If you write text at BGG, you might want to read this list.
This article was inspired by the thread I don't mean to come off as a grammar Nazi but...
accept/except: to accept an offer; everything except that
advice/advise: to give advice = to advise
affect/effect: to affect something = have an effect on something
allowed/aloud: allowed = permitted; aloud = audibly, not silently
asymmetric: there is no "ass" in "asymmetry"
biannual/biennial/semiannual: biannual is unfortunately overloaded to mean "every half year" (its original meaning) OR "every two years"; biennial = "every two years"; semiannual = "every half year"
capital/capitol: capital is a city, capitol a building
cavalry/Calvary: infantry, cavalry, artillery; Jesus was crucified on Calvary
coming: it's not spelled "comming"
congratulations: it's not spelled "congradulations"
could have, should have, would have: the phrases are not "could of, should of, would of"
could've, should've, would've: contractions of "could have, should have, would have"; they are not spelled "could of, should of, would of"
couldn't care less: it's not "could care less" (which implies you care at least a little); Handy chart illustrates the principle!
decent/descent: decent = fairly good; descent = downward movement and game title
definitely: it's not spelled "definately"
die/dice: 1 die; 2 dice. Note: British English apparently considers "dice" to be both singular and plural, although there are very few such English words besides some animals like fish, sheep, ..., and the famous quote by Caesar is usually translated as "The die is cast", not "The dice is cast"!
dominant/dominate: a dominant person dominates others
fiancé/fiancée: a fiancé is a man; a fiancée is a woman
finish/finnish: start/finish; Finnish/Finland
for all intents and purposes: is the proper idiom, not "for all intensive purposes"
gantlet/gauntlet: running the gantlet (an ordeal); gauntlet = armored glove. But most dictionaries agree the two words have been confused for so long that they may be interchangeable. http://en.wikipedia.org/wiki/Running_the_gauntlet
grammar: it's not spelled "grammer"
I/me: Don't use subject pronouns as an object. Correct: He likes my wife and me. They ate with my wife and me. ...to my brother and me. ...for my family and me. Incorrect: He likes my wife and I. They ate with my wife and I. ...to my brother and I. ...for my family and I.
imply/infer: imply = suggest, insinuate (when I say something, I can be implying something else); infer = deduce, suppose (when I say something, you can infer something from it)
independent: it's not spelled "independant"
its/it's: the dog likes its food; it's = it is
kibitz/kibbutz: people kibitz about what's happening in a game; Israeli collective farmers live in a kibbutz
lose/loose: win/lose; tight/loose
mechanic/mechanics/mechanism: The correctness of "a game mechanic" is often debated at BGG. Some say that mechanic = person who works on machines; mechanics = study of mechanisms; mechanism = machine/instrument/process. So "game mechanic" is arguably retrofitted from the singular but plural-looking "mechanics" (few people would say "mathematic" from "mathematics") when one probably should use "game mechanism". But others point out that this use of singular mechanic actually is centuries old, and the Oxford English Dictionary gives "mechanism" as one definition of "mechanic" and quotes Francis Bacon from 1605: "The fault being in the very frame and Mechanicke of the parte". So "game mechanic" is arguably OK.
naval/navel: naval ships in the navy; navel = belly button, navel gazing
Nazi: using "Nazi" in a trivialized metaphor like "Grammar Nazi" can be offensive to some. Complaining about people using "Nazi" in a trivialized metaphor like "Grammar Nazi" can be offensive to others.
poor/pore/pour: poor = not rich; pore over something = study it carefully; pour a liquid
rein/reign: reins restrict or restrain (e.g. a horse); a king reigns over a land. "give free rein", not "give free reign".
ridiculous: it's not spelled "rediculous"
rogue/rouge: rogue = sneaky person; rouge = red makeup, or French for red.
role/roll: role-playing; roll the dice
rout/route: a rout is a disorderly retreat (as in many wargames); a route is a road or itinerary
sight/site: sight = vision; site = place, such as a website
secede/succeed: The Confederacy seceded from the Union; they did not succeed.
secession/succession: The US Civil War was a war of secession; a war of succession is typically about who will succeed (take the place of) a recently dead leader.
solitaire: it's not spelled "solotaire"
suit/suite: 4 card suits = ♠♡♢♣ or a business suit (jacket and pants); suite = collection (of software, furniture, music, hotel rooms, etc)
their/there/they're: they like their food; here, there, and everywhere; they're = they are
to/too: go to the store; Space Hulk is too expensive or I will be there too
who's/whose: who's = who is ("a player who's losing"); "whose" is possessive ("a player whose position was hopeless")
y'all: "you all" is contracted to "y'all"; it's not spelled "ya'll"
your/you're: you like your food; you're = you are