I wonder if it would be worth it to go through very often.
Presumably the free books tend to stay free, and you'd just be catching the small percent that have temporarily dropped to free on a promotion, and you'd have to sift through all the ones you've seen before over and over.
Better to use a service that just shows the newly free ones (I've run across some in passing).
This is definitely worth an initial look and download for anything interesting, and probably worth checking every... 6 months, maybe 1 year. Too often and you run into the "all these books are the same" problem as above (and in a year your tastes might change a bit so you download stuff that you wouldn't have a year before).
