I have always been scared of that kind of thing, though in the end it never happened to me. So it is a thing then?
I've not heard of it happening to anyone in recent years, but Network Solutions were definitely accused of it in 2009, using the 5-day "tasting" period. See http://en.wikipedia.org/wiki/Domain_tasting#Anti-Domain_Tast... for a mention. I would very be surprised to find that it doesn't go on in various places to this day, so for paranoia's sake only search for names you want using known reputable providers.
Way back in is mists of time (~1999/2000, while at University) I had it done to me. We were going to register a name for our student house (and a few other people) and searched for two options both of which were available at the time. A week later when we came back both were registered by the same individual (not directly linked to the company from what we could gather) with a "buy this domain! (for several times the usual cost)" page present. This could have been a coincidence of course, so we looked up a collection of other convincingly real names (from various locations so it wasn't a block of lookups from the same address). A short while later they were all registered the same way, and not on the "5 day" thing either because they all still were a while later. We could have been cruel and search a great many more (had we actually cared about the name(s) we "lost" we might have done) to waste their money but didn't as we had far more important and/or fun things to be getting on with at the time.
I just go to register as soon as I'm sure I would like the domain name. That way, worst case it's already registered, best case there's minimal opportunity for front runners.
Even trying it in a browser might alert someone monitoring DNS for interesting NXDOMAIN replies. (Yes, this may be paranoid, but it's hard to keep up with the nefarious tricks that actually go on)
Use a reputable registrar for searching, even better become a reseller and do it via your reseller account.
Unless there are specific rules against it, I could see this becoming worse with all the new TLDs.