In snapshot 14w28b, even when using CanPlaceOn and CanDestroy NBT tags in Adventure mode, it is impossible to use a hoe to till dirt or grass blocks.
To reproduce:
/give @p wooden_hoe 1 0

{CanDestroy:[dirt,grass],CanPlaceOn:[dirt,grass]}

In adventure mode, the hoe will not be able to till dirt for grass blocks.
In the same snapshot, one also cannot plant seeds of any kind on tilled soil.
To reproduce:
/give @p wheat_seeds 1 0

{CanDestroy:[farmland],CanPlaceOn:[farmland]}

Then, in adventure mode, try to plant the seeds. Good luck.
Furthermore, one cannot pick up water or lava with a bucket.