Well I do think it is better than leaving the gun out on the TV table next to the big living room chair or atop the night stand next to the bed.
I also think it depends on the house. I have done it but do not currently. At 25 as a college student on the GI bill I did not have much extra cash. I saw a under grade Western civ text that blended right in with my school books and cut it up for a safe for a revolver that did not get locked away and stayed close to my bed and study area. It thus did not stick out with a weird title or subject and looked like it was supposed to be there. Now if there were three or four books on a night stand and I was tossing the place as a crook, I sure would look there. If nothing else it is just the sort of place folks stash a few loose bills of cash or the very hollowed out book you mention. On the other hand if it is a four shelve book case crammed full between the bed and desk A crook might not take the time to look.
For a bit when we lived in town I did keep such a book safe in the book case closes to the door. Between the three of us we only had about 2000 books and eight six foot high book cases bolted to the wall though. Again not quite the odd book title among three or four books near the master's throne.
For a bit while the wife was in law school the house gun nearest the front door was in a nylon holster safety pinned well down the arm of the couch next to the door. At her graduation party with the house full of just hatched lawyers a thug showed up and demanded what we had and threatened violence. You should have seen the expressions on the guests' faces when I asked one to lean away from the arm of the couch, bent over and retrieved a semi auto pistol and explained life the universe and everything to our would be bandit. "Priceless"
For a bit a lady I knew when I was at Florida State had a holster duck taped under a coffee table with drop sides and in the holster was a Charter undercover .38 Special. It made it through several parties with out being noticed.
Keep in mind that in some states if you have underaged folks in your home that un locked guns are a no-no.
Seriously if at all possible consider some sort of locking steel box that can be affixed to an immovable object and leave the hollow books and furnature voids to the long dead past ......if at all possible.
-kBob