“Thanks for that”

As this is mainly conversational, this will be a very difficult one to prove either way, but I would have though that both uses have been around for quite a long time.

At the British National Corpus (mainly from the 80s and 90s) there are about a dozen instances of 'thanks for that' - several of radio DJs thanking callers, and a couple from training sessions, thanking people for their input, where I presume no irony is intended (you can click on the numbers to see the source):

'Right, thanks for that, we'll, we'll come back to that. '
'Thanks for that group. '
'Oh that will be splendid er well thanks for that, that's er that's great obviously'

There are a couple with the meaning you suggest:

'Well, thanks for that,’ he murmured drily. '

But there are also occasions when it is followed by a noun with this meaning:

' ‘Well, thanks for that brilliant piece of help,’ he sneered. '

So at the BNC, at least, the majority seem to be in the non-ironical sense. And I would go along with that - when thanking someone for contributing to a discussion, or for giving a piece of information, in a meeting for example, 'thanks for that' without any loaded extra meaning is quite normal, as is using it to thank someone who has just done something for you when it is obvious what 'that' is referring to. It all depends on context and intonation - in your meaning it would probably go down at the end; in the straight meaning, it's more likely to go up.

http://bnc.bl.uk/saraWeb.php?qy=thanks+for+that&mysubmit=Go

Early examples at Google Books not prefaced by 'We give thee' are rare, but those that do exist don't seem to have the ironic sense:

'Thanks — thanks for that !" exclaimed the Aztec, drawing the priest more closely to him ; and, with a confidence worthy a truer heart than that which received it, laying his head on his bosom ; " Thanks for that ! It tells me, my gods have still a ...' - Montezuma, a Romance, Edward Maturin , 1845

'Thanks for that, my pet ; so must a reasonable maiden think. Fill your glasses. Long life to the bride, and the bridegroom too !' - (a father talking to his daughter) - The Gift: a Christmas and New Year's Present ', edited by Eliza Leslie, 1845.

' “Thanks for that,” said Lord de Yonge, with something of ecstasy. “Thanks for that. Now let that villain do his worst; the Lord Chancellor of England is now the exclusive guardian.', The Two Cosmos: A Tale of Fifty Years Ago, 1861.

And then there's Shakespeare -'Thanks for that', Macbeth to the First Murderer after he has killed Banquo on Macbeth's orders, presumably sincerely.

So yes, it often was intended as put down, but my impression is that it has always been used in its straight sense as well. And the put down could just as easily include a noun phrase:

"Thanks for that piece of scintillating information!"
"Well, thanks for that remark, it was really helpful. Not!"

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