Thought I'd share this, after experiencing a pretty useless 'best rate guarantee' experience with Hilton, compared to a much better experience I have had with Sheraton...
I made a booking with hilton.com for the Hilton in Eilat, Israel. Afterwards, I found a cheaper rate on an Israeli website (http://www.queeneilathotel.co.il/heb/). I filled in the BRG request, and a few days later I got a response telling me that the rate was not comparable because the other website was for Israeli citizens only. Now, I couldn't find anything to that effect on the website, but assumed the BRG folk knew what they were talking about. I told them that I couldn't see this, but in any case, I was an Israeli citizen. They wrote back a couple of days later stating that this means the T&Cs are different and therefore the BRG doesn't apply. Seemed pretty nit-picking to me.
So I cancelled my original booking and booked with the Israeli website. Not once during the booking was I asked whether I was an Israeli citizen or was required to fill in information that only citizens have. Nor could I find such a mention in the T&C.
As a result, Hilton made me realise that the BRG isn't really worth much, and they probably spent more effort writing their emails then giving me the ~$110 off I was asking for (across the whole booking).
I compare this to an experience I had with Sheraton not long ago - where the BRG was honoured immediately without questions once I found a cheaper price on another site...