What happens after 20K books? I am at about 13K books, and I haven't run into any issues yet. I make extensive use of virtual libraries in Calibre, and tags for organization.
I use goodreader on the iPad the same way you use textbooks. Only on the PDFs, but you can type, highlight, write, scribble draw all over the PDF. One feature that I like is I can then export just the typed up notes, so I have my own kind of cliff notes version of a book. Good if you follow the 'How to read a book' methodology.
Ha! I swear to god, I will read those Knuths one day even if it kills me. I have travelled a good portion of this planet, and the one thing that has always travelled with me is my 3 volume set of TAOCP. They've frozen in a tent with me in Alaska, been homeless with me in Hawaii, seen the rocky mountains and are currently chilling with me in central Europe.
I have to say one of the main reasons for this is that they are beautiful books. The design and printing of them are awesome, I even used them as inspiration for designing my friends first novel (self published) which took me six months of researching typesetting and fonts and hacking away on InDesign. I don't think I could ever bring myself to throwing/giving them away.
But I've never really had the chance to use them for posturing, non of my meatspace friends are remotely involved in IT, so have no idea about the books. But many a person has been impressed by the aesthetic quality of them, believe it or not...