Multiple Contractions

A short time ago I came across the word I'd've.  At first I was somewhat taken aback!  I had never seen a word quite like this before.  I had never even considered writing a word with two apostrophes.  It was easy enough to understand as "I would have", but I still wondered whether this type of contractionizing happened often.

After some searching around it seems like my experience has been fairly common.  People agree that it's used somewhat in spoken language, but rarely if ever written down and never in formal writing.

Of course why stop at I'd've?  How about couldn't've or she'd've.  And why stop at double contractions?  How about triple contractions like I'dn't've or you'dn't've!