I'm tempted to say that taint mode should be the default in perl, just on the grounds that it has kept me from doing hell of a lot more idiotic things then use strict; has. but with a tool that is trusted this much you need to remember to check yourself over as good measure, case in point:
one script i wrote used taint mode but i wanted to convert a few fields to lowercase before i fiddled with them, after 'untainting' all of the scalars by tr /A-Z/a-z/ suddenly my data was ok and i forgot to actually check the value till about 3 days before it went out, and then i only caught it by accident......

taint mode rules, cause it forces you to be careful... so i would recomend it. however, remember the story and dont forget that taint mode doesnt know the difference between a smart and a dumb taint check.
jcpunk

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all code is tested, and doesn't work so there :p (varient on common PM sig for my own ammusment)