yea we get thet too - and the press will regularly say - can we colour match that and print it as a solid - as opposed to 2 (or more) colours....then i have to think for a living and make it happen - which usually hurts
i dont "get" designers doing that either - then again we are packaging and we have the flexibility to change stuff but i bet those of you that dont and have to go with it have issues keeping consistent colour sometimes - its a pain huh
we work with overprint preview almost always on - in illy, indy and acrobat (sigh - but not quark) and it's invaluable - until one day, after printing these cartons many many times, the customer casually asked "where's that white line of text"
"what white text" i asked.......only to find white text set to overprint - which we couldnt see as we were viewing in overprint mode

ops:
they were very good about it, conceeding it was set up wrong and all proofs were signed off and press passes done - we conceeded we should have spotted it - so somewhere in your "workflow" make some provision for checking for "white overprints"