Yes, I am concerned. For the convenience of customers, I keep everything but houses rezzed, even though it costs me a lot of prims to do so. However, that makes me even more vulnerable to theft, as thieves can copy anything that is rezzed. That’s not to say that clothes, skins, shoes, etc. are not vulnerable, because they can be stolen literally off your avi’s back.
Thieves justify their thievery in a number of ways, but it boils down to creators not being entitled to reap the rewards of their labor — somehow, the thieves are entitled to those rewards. Sometimes people ask me if I really made everything in my store. Yes, I made every stick, all by myself, plus a whole lot more in inventory that I don’t have room for. I do all the customer support, advertising, etc. You can imagine how many thousands of hours that has taken, and how it must feel to see someone else reap the rewards for those hours.
There are a number of things that can be done to reduce theft by making it more inconvenient, but nothing that can prevent it. Nothing. What we all can do, however, is be on the lookout for stolen merchandise, because SL and Xstreet are full of it (and now, so are websites outside of SL). There are whole stores, even whole sims, that are nothing but stolen merchandise.
When you see something that does not look right, notify the original creator, or whomever you think the original creator might be. Think carefully before buying that super-cheap (or free) item from someone that seems to sell ONLY this sort of thing. For example, the Xstreet listing for 12 very nice FULL PERM hairs for 295L? All stolen, of course, from easily recognized creators.