Hey Mark Chance, you're a punny guy!
And I gotta agree with the repelling dogs thing....
But, to answer the question... (first off, I don't have my books handy so I can't re-read it). I am pretty sure you can still observe the surroundings - Druidic voyerism
Some uses that come to mind...
Hide in a forest
Spy on a nearby encampment/structure/settlment
As for casting spells and the like, I would wager that most components are out:
V ('cause you can't speak)
S ('cause you can't move)
M ('cause you can't manipulate the M)
F ('cause, again, you can't manipulate the F. and it specifically says in the components description that you must manipulate an F component)
DF - this is slightly tricky. It really does fall into the same catagory as the F. However, I keep thinking I saw in the FAQ or an "Ask the Sage" that DFs can be on a person, like a pendant on a necklace or an emblem on a shield, for instance. So this component may work if the DF is hanging on the tree form somewhere
Now if you have the silent and still feats (and whatever else that removes the necessity of various components) you could probably cast just fine sine (I believe) your mind is still in tact.
You can't move, being a tree and all... maybe just sway a little.