A person that desided to switch between squid and
squid-novm and removes one of them before installing
another will be very happy to discover that his/her whole
cache is gone.
I know that a heavily loaded squid will probably regenerate
cache in several hours, but it may take several weeks or
even months for a lightly loaded cache to get back to its
original HIT ratio after a cache loss.
(assuming you mean *not* very happy :) )
Fixed in squid-2.1.PATCH2-3. Also, logs are no longer deleted