I think it's whatever you'd think it's weakness would be, only highly magnified. For example, it's commonly thought fire release is the counter to ice release, however Haku proved otherwise. It must be remembered though that that was very early in the series. Powerful katon techniques, like Great Fire Annihilation, would have a higher chance of blasting right through ice release. Dust release might be a little difficult to determine as it doesn't really have a physical form that's counterable. Additionally, it atomizes whatever becomes trapped within it.