We have been using pZeroI for a couple of months and have had excellent
results. I made a partial Sau3A1 library in this vector and nearly 90%
of the colonies contained inserts of the correct size. I think the time
and problems involved screening lots of colonies and/or using CIAP makes
it very worthwhile to use pZeroI. It is important to follow their
instructions about using low salt LB for plating out transformed cells
and growing colonies in SOB + Zeocin; otherwise, the vector and strains
transformed with it behave normally.
I've heard that other researchers have used bleomycin from Sigma in
place of Zeocin (which is simply purified bleomycin). However, I also
found out from Invitrogen that you can use 25 ug/ml Zeocin to select for
transformants in E. coli, even though they say to use 50 ug/ml in their
pZeroI manual, so you can cut down your antibiotic costs considerably
if it is a problem.