My wife and I each had a copy of the first three volumes when we married. Yes, there are female computer nerds. B-)
I first encountered it when assigned one of the volumes as a text back in 1971. Of course the class didn't consist of learning EVERYTHING in the volume. B-)
I use it from time to time - mainly as a reference book. Most recently this spring, when I needed a reference on a data structure (circular linked lists) for a paper. I've found it useful often when doing professional computer programming and hardware design (for instance, where the hardware has to support some software algorithm efficiently, or efficient algorithms in driver software allow hardware simplification).
I don't try to read it straight through. But when I need a algorithm for some job and it's not immediately obvious which is best, the first place I check is Knuth. He usually has a clear description of some darned good wheel that was already invented decades ago, analyzed to a fare-thee-well.
I only see him about once a year. He's still a sharp cookie.