I find katakanas harder than kanji sometimes like there was this song that says "furette", it was written in katakana and I kept on wondering what it means. When I Googled it, Google says taht it means "hooray"...
Then there was this other time when I read one of AKB48's song titled labrador retriever taht is written in katakana again, I read that one as "love radar retrieval"... Why do you Japanese love these complicated writings?XD And why did I bothered studying them? XD
In many cases, the purpose of katakana is to indicate the sound of words. But I know, foreigners feel that it is very strange :)