Fillers aren't a problem really, provided they're done well. Like Kyubi pointed out, single episodes that provide a bit of comic relief can be good. It also helps if they fall in between series arcs.
But, especially in longer series (aka Bleach, Naruto) they do them really badly - and can totally put me off a series - like in Bleach, where, smack bang in the middle of the arc, the story gets interrupted by 5 or 6 episodes of absolute trash.




