"It'd better be good" and "It better be good"

So! My question is this: is "it better be good" grammatically incorrect (I don't see how...)? Or are both of them correct but have different meanings? My theory is that both of them are correct but "it better be good" is a command where as "it'd better be good" carries a subjunctive mood...

And here comes Question 2! After being picked on "it better be" I was also accused for writing "it is indeed".  In fact, my "it is indeed" has been corrected to "yes indeed".  I'm pretty sure indeed is an adverb and so is yes.  So how is it possible that "yes indeed" (without a comma) is more correct (excuse me) than "It is indeed"? I know my grammar isn't perfect but I'd be a tad bit less upset if I were corrected with "yes, indeed" (with a comma).

Thanks in advance! (<----- here comes my third question, some people say "thanks in advanced" and others say what I said.  Which one is correct?)

Here's how I see things.

1. "It better be good" is not grammatically correct, but people say it a lot anyway. It is said so often that it seems to have become a standard phrase.  Maybe people see the missing "had" as understood. "It'd (or it had) better be good" is the grammatically correct form. I wouldn't worry if someone used the first form of the sentence, though.

2. "Yes, indeed." "It is indeed" the case! Depending on circumstances, either or both could be correct. (Are you tired? "Yes, indeed.") (Is it time to go to sleep? "Yes, indeed." OR "It is indeed." Both phrases work in this example.) (At the moment, I can't think of an example where only "It is indeed" would work.)

3.  "In advance" is correct and means before, earlier than, ahead of time. You are thanking people before they answer (and encouraging them to respond). (Someone might say "In advanced English classes, it is important to read a lot." This would be correct usage of "in advanced," but the meaning would be different.)

I think one of the most difficult things about using a second or third language is knowing how much leeway is acceptable, understanding what kind of possible mistakes are real problems and which are so minor (or debatable) that they really aren't worth much attention. Of the examples you mentioned, the only one that would make me uncomfortable would be the "in advanced" phrase. That would grate on my ear (sound very wrong).