That's okay' vs. 'It's okay'

[wwwilder1]

Looking for a succinct, definitive answer to the question what's the difference between 'That's okay' and 'It's okay'?

Here are some examples....What are the rules?

-Sorry for being late.
It's okay. (It's not a problem.) That's okay (Not to worry.) -- Both appropriate?
-I couldn't do it. That's okay. (Not to worry.) --'It's okay' not appropriate?
-How was the food at ABC restaurant? or Is your foot okay? --> It's okay. (The quality is okay.) 'That's okay' not appropriate?

Another example: Subordinate talking to a boss about vacation:

S: I'm thinking about taking the first two weeks of September off to go to Bali.
-- Is that okay?
--Is it okay?
The boss would answer either way depending on how the question was asked, i.e.,"Is that okay?", the answer should be "That's okay."....

Anybody have a link to a resource where the diff. is explained or can anybody explain it?

[fluffyhamster]

You could get around it by teaching "S'okay".

Sorry, but I don't know of any links offhand and wouldn't have the time to explain things even if I fully knew how to (am in a net cafe right now with limited time remaining), but there should be something about it in Carter and McCarthy's new grammar (The Cambridge Grammar of English), and probably in the likes of Swan (Practical English Usage 3rd edn) too, if your school, a colleague, or a bookstore near you has a copy.

[Stephen Jones]

Don't think there's any difference at all.

[fluffyhamster]

Yeah, not much point in sweating it too much, as SJ says. My mind went off at a bit off a tangent 'cos students (and non-native teachers) at my school had been going through basic deixis Q&A in relation to hazy objects, strangers etc, which isn't quite what the OP was asking about.

[Anuradha Chepur]

With the don't mind/you don't worry connotion, both choices are interchangeagble.

With somehting is good/alright connotion, I don't think you can say that's okay.