Listening to people around Beijing over the past few days, I've noticed a couple of things about a common Chinese word. The Wiktionary gloss for 对 (dui4) suggests the pattern:
Yes! Correct! I agree!; The word is used often in spoken language. It is common to repeat the word three times when you want to make clear that you understand and agree.
My impression is that a single duì is common, and three-fold repetition is also common, and sometimes even five in a row (grouped 3+2?), but not two or four. (I think I heard a double duì once, but it was more like two phrases "duì, duì".)
I also got the impression of a gender association: triple duì seemed common in women's speech, but I don't think I heard a man say it. Of course, this could be a random consequence of the small sample particular people that I was with — colleagues, their students, taxi drivers, passers-by talking on cell phones, etc.
I might have been tempted to infer something about the metrical organization of vernacular Mandarin, but 是 shi4, which the Wiktionary glosses (among other things) as "yes (as answer to a question)", seems very often to be doubled "是是", and more rarely triple.
One other interesting thing about 对 dui4 is variation in its pronunciation. The Wikipedia article on pinyin give the pronunciation of ui as [u̯eɪ̯], but the Wikipedia pronunciation
and the Mandarintools pronunciation
both hint that the high back vowel is the nucleus of the syllable, with the [eɪ] part being an off-glide. I got that impression even more strongly in hearing it used, with nucleus a bit lowered and the off-glide fairly short, something like [doɪ]. One speaker even seemed to omit the high front off-glide entirely in producing a five-fold string like [dododododo].
On the other hand, single repetitions of 对 dui4 sometimes seem to shift the nucleus to the second part of the syllable, something like [dwe:], with the vocal part sounding quite a lot like the French vernacular pronunciation of oui often written as "ouais".
I have the feeling that these variations in the vocalic part of 对 dui4 are the sort of thing where the IPA forces us to categorize what is really a more gradient sort of variation.
Anyhow, I don't have a lot of confidence in the validity of these impressions, except as reinforcement for the obvious idea there are a lot of things to be learned about sociolinguistic variation in Chinese.