Most people, especially writers, have language pet peeves. I probably have more than most. The top of my list, though, is when people misuse “then” as a substitute for “than.”
Examples:
- “I like GNOME more then KDE.”
- “when a file is zipped for more then X times”
Both are incorrect. They should be using “than,” not “then”. For some reason, I rarely see people using “than” in place of “then.”
How to keep then and than straight:
Then is usually related to time or as a way of qualifying a statement. Examples of correct usage:
- John had a horrible cake-related accident in 5th grade. Since then he’s been utterly terrified of chocolate cake.
- If you think you’re so smart, then you defuse the bomb and I’ll be 1,000 yards away.
- I’d rather watch two hours of infomercials than have to sit through that movie again.
Note: Yes, if you go back far enough, then seems to have evolved from than. But something tells me that’s not the origin of this mistake as that usage is centuries old.
This is something I’d never really seen in common usage prior to about 2002. Maybe I just didn’t notice it. But it seems to be perpetuating itself via the Internet, and has even been creeping into print.
Do a Google search for “more then” and you’ll find “about 27,000,000″ results. Yikes! Thank goodness, so far “more than” turns up “about 271,000,000″ results — getting it right is still the norm. Let’s keep it that way.
Another mistake I see/hear often these days is the use of the expression “flush out” in place of “flesh out”. An idea or concept should be “fleshed out”, while the toxins in one’s body should be “flushed out”.
@akbrown Whoa. Yeah! I haven’t seen that one myself, but that’s a whole new meaning if you want to “flush out,” an idea.
Some ideas should be flushed, but I don’t think that’s what they mean to say. 
“Than” is used to join two clauses in a comparative manner. Often the predicate and even subject in the second clause is implied. “I like fish more than (I like) meat.” “I run faster than he (runs / does).” I think this is the key definition of the word.
“Then” is used to join two events of different times as you said, and also to refer to a time in the past or future (akin to “next” or “later” when used for future reference). “I ate, then I slept.” “I will eat, then I will sleep.” “If you have a better definition than I, then leave a comment.”
@Jonathan Thanks for the additional info!
How about addressing the “try to” vs “try and” errors. That’s a huge pet peeve for me. Either tell me that you are going to “try to” do something, or tell me that you are going to do it. But don’t tell me that you are going to “try and” do something. If you do it, I will assume that you tried before you actually accomplished it. GRRRR!!!