I've just found the quote in question, the one from the new £10 note. It's in chapter 11 of P&P. As it turns out, it comes just
before the exchange I was initially remembering, where Caroline Bingley and Elizabeth are strolling around the room and trying to tease Darcy. Prior to that, after those at Netherfield have finished their tea, "Darcy took up a book; Miss Bingley did the same" — and the following ensues:
Miss Bingley's attention was quite as much engaged in watching Mr Darcy's progress through his book, as in reading her own; and she was perpetually either making some enquiry, or looking at his page. She could not win him, however, to any conversation; he merely answered her question, and read on. At length, quite exhausted by the attempt to be amused with her own book, which she had only chosen because it was the second volume of his, she gave a great yawn and said, "How pleasant it is to spend an evening in this way! I declare after all there is no enjoyment like reading! How much sooner one tires of anything than of a book! — When I have a house of my own, I shall be miserable if I have not an excellent library."
(The last line, of course, being because she knows very well that Darcy has an "excellent library" at Pemberley!
)
Having re-read that in full, I can see why some fans don't think it's appropriate to have it on the £10 note as if it were something Jane herself said and meant at face value — rather than being, as it is, a quote from one of her characters who is vain and shallow and is only pretending to love reading in a blatant attempt to gain a certain gentleman's attention (and he's much too smart to fall for it). But it's probably safe to assume that Jane
did find great enjoyment in reading, so it's not all that misleading a quote, really.