Let's just say that not using it will cause more trouble than it's worth, and that if the option should eventually disappear or change it shouldn't be much work to change your code to adapt. Database drivers don't update themselves; just check when you install a new version.

You should assume that all code using utf-8 with DBD::mysql on current versions will work better when that option is used. I'm using it in a couple of fairly large systems and the only real issue I've had is that it's not complete - you still have to make sure data specified for UTF-8 columns is really utf-8 before sending queries.

Since 4.004 using the option will as far as I know at least guarantee you'll get your data back with correct status for the utf-8 marker of each column, for every type of column. Nothing else will give you that guarantee.