I agree with Andem. Scrapers CAN hurt you despite your making smart moves and optimization. I do agree it's possible to focus too much on them, and it's wise to consider which ones are really capable of hurting you before spending effort on C&Ds (not that it takes much time to do C&Ds - I can fire off 5 in twenty minutes, and most of the time, they're complied with).
It's also important to consider other options for defeating scrapers. Since I switched from full to excerpt feeds, I've had no scrapers at all - just a handful of manual copies of my articles. Sometimes I C&D them - but sometimes I look at my article and see room for improvement, and just end up rewriting it significantly. (But I post both the original copyright date and the "updated" date on every page, just in case.) This tactic makes my site more valuable, which is what it's really all about, after all.
So yeah, they can hurt you, but drowning in C&D work isn't necessarily the best use of your time and energy.