I don't think f/a's are worried about terrorists locating them at a hotel. As someone else said earlier, it's more the wackos and stalkers they worry about. There have been instances in the past where f/a's were tracked down by passengers, but I think they're pretty rare. Rare or not, all you need is to hear a couple of the stories and you would become tight lipped too. I have a friend that was almost beaten to death several years ago in a hotel from someone that had asked her where they stayed. There was also another case where someone asked the f/a's what hotel they stayed at in a certain city; they weren't stalking anyone on that crew, but they were after someone that was going to overnight there a couple of nights later. Less dangerous and more annoying are the ones that do find out your first name and your hotel and then call you all night, either as a joke or being malicious. That being said, there are tactful ways for not telling someone our accommodations. I will usually say very vaguely that I think we stay some place near the airport but I can't remember what hotel, or I think we've changed hotels and I'm not really sure where we stay. There's no reason to be rude about it, I think a high percentage of the people that ask are completely innocent.
As far as complaints go, if you don't have a f/a's name then I would suggest writing down the flight number, the date and a brief description of the f/a. If you were talking about me you could simply say "the drop dead gorgeous bombshell" and they would immediately know you were talking about Galley Wench.
Just kidding...By looking at a trip pairing the company has no way or knowing where a particular f/a worked, we change positions all the time.
Put yourself in the f/a's shoes for a minute. If a stranger sitting next to you asked specifically where you were staying that night would you tell them? Some might say yes of course, while others might be more cautious. F/a's basically feel the same way, some will tell and others won't.