I hope someone corrects me if i'm wrong but I had read it was mostly a dialect! There are many other 'colloquial' modifications to words... A search in google yielded this: http://en.wikipedia.org/wiki/Kansai_dialect#Adjectives extract: The stem of adjective forms in Kansai-ben is generally the same as in Standard Japanese, excepting regional vocabulary differences. The -i ending can be dropped and the last vowel of the adjective's stem can be stretched out for a second mora, sometimes with a tonal change for emphasis. By this process omoshiroi "interesting, funny" becomes omoshirō, and atsui "hot" becomes atsū. This usage of the adjective's stem, often as an exclamation, is common throughout the entire history of the Japanese language; it is seen in old literature in Classical Japanese, as well as many dialects of modern Japanese (Some dialects including Kantō are more likely to elide the adjectival ending into the last vowel of the stem, yielding omoshirē and atsī or achī for the above examples).

Yes, this is right. In Kyushu, this is a common sound change which sounds masculine (but girls can use it too). The one I hear the most is "suge" short for "sugoi". Children use it all the time, but sometimes I hear adults using it. I think this slang is nationwide, but I'm not sure about "kakke", the one you mentioned. I haven't heard it in Kyushu. I guess it's kinda like modifying "cool" into "kewl" or something. Just a sound change.