  As it follows from the classical analysis, the typical final state of the
dark energy universe where dominant energy condition is violated is finite
time, sudden future singularity (Big Rip). For a number of dark energy
universes (including scalar phantom and effective phantom theories as well as
specific quintessence model) we demonstrate that quantum effects play the
dominant role near Big Rip, driving the universe out of future singularity (or,
at least, making it milder). As a consequence, the entropy bounds with quantum
corrections become well-defined near Big Rip. Similarly, black holes mass loss
due to phantom accretion is not so dramatic as it was expected: masses do not
vanish to zero due to transient character of phantom evolution stage. Some
examples of cosmological evolution for negative, time-dependent equation of
state are also considered with the same conclusions. The application of
negative entropy (or negative temparature) occurence in the phantom
thermodynamics is briefly discussed.
