I've found that it's just a stylistic choice to add effect to what they're writing. You wouldn't find it in a really formal text. It's like a fad that's widely used within Japanese society.

I precisely agree with Dawn. Let's one thing straight, refer to "おウチ", I neither write nor saw written in katakana like that.

キライis more casual and　嫌い is more formal I think. You wouldn't write キライ　in formal writing. キライ sounds lighter and 嫌いsounds more serious. キライ sounds more girly or childish and 嫌い sounds more manly. ただただsounds more frank, 只々sounds more serious. sometimes older people uses kanji more and younger people use katakana more.