1. its hard to find, and when you do find it you have no control over the colour, thickness or quantity.
2. when you manage to find a suitable colour it will not have any complementary colours with it, so if you want different tones you have to dye it.
3. dying wool is not easy or predictable. plus it felts half the time.
4. its expensive, which means you have less room for error. plus its harder to build up a 'stash'.
ok. thats my first four. i'm sure there will be more to follow. i'm a bit fed up after spending hours yesterday dying fabric with not much to show for it.
still think its worth it :)