I could give you a lot of reasons why I personally don't like them but they all have to do with boring music industry politics (I work in the music industry - it leaves you jaded and resentful against many things!) But mainly it's because of their marketing strategy (well not McFly's, their managements's - I don't have anything against the boys personally.) Some stuff came out around McFly and Busted's marketing a few months ago and it just made me shake my head in sadness. The music's pretty diabolical as well but that comes from someone who's a big fan of real rock music.
However strangely I do like a few of Busted's songs, go figure!!!