already true in particle physics (Score 1)

I work in particle physics and e-prints (electronic preprints) have been the standard
way of communicating work for the past few years.
( See http://xxx.lanl.gov/ ). It's still usual to submit to a paper journal, but after the e-print submission. The paper journals do still perform a usefull service however, because the submissions are then sent out for peer review, so the final
paper version may be of higher quality (although
the changed versions are usually re-submitted to
the e-print archive). It also looks better on future jobs applications to have papers accepted
by established journals.

The one example I know of an all-electronic
refereed journal is http://jhep.mse.jhu.edu/
but it hasn't really managed to build up it's
reputation to the level that it needs to compete
with the paper journals.