Quote from TXMount
It's been a while since I Thaumed, but if I recall correctly, the portable hole was stopped horizontally by chests, signs, ladders, and Seals. Trying to Hole through a wall with one of those items in the way would fail, and give an error. I vaguely recall that the Hole is foiled by flowing liquid as well.. One of my standard base-security measures is putting the entrance underwater (to keep out the zombies) and I had huge problems trying to adapt a Hole-based exit strategy into a liquid environment.. I *think* Holing vertically was stopped by halfblocks and pressure plates, but I admit that I didn't do a lot of testing on it, because I kept making the hole too long, and falling through my lab into the magma pits under it.... The Portable Hole also only removes the blocks temporarily.. the time seems to be related to the length of the hole -- longer holes stay around longer.
Incidentally, a fun/stupid trick is to Hole a tree from directly underneath. As long as the wood is "gone," the leaves will be subject to leaf-decay... It's an absurdly amusing way to strip the leaves off IC2 Rubber trees, so you can see the sweet, sweet sap holes.
I agree that does seem fun, a better way to clear off the leaves. But with rp2 just around the corner, the sickle also does leaves now. So i will be using that.