  Various aspects of distillation of noisy entanglement and some associated
effects in quantum error correction are considered. In particular we prove that
if only one--way classical communication (from Alice to Bob) is allowed and the
shared $d \otimes d$ state is not pure then there is a threshold for optimal
entanglement fraction $F$ of the state (being an overlap between the shared
state and symmetric maximally entangled state) which can be obtained in single
copy distillation process. This implies that to get (probabilistically)
arbitrary good conclusive teleportation via mixed state at least one classical
bit of backward communication (for Bob to Alice) has to be sent. We provide
several other threshold properties in this context including in particular the
existence of ultimate threshold of optimal $F$ for states of full rank. Finally
the threshold results are linked to those of error correction. Namely it is
pointed out that in quantum computer working on fixed number of quantum bits
almost any kind of noise can be (probabilistically) corrected only to some
threshold error bar though there are some (rare) exceptions.
