In reply to elliot.baker:
I think it very much depends on how you descend. If you thud down without thinking about form and technique then I'd say yes it's going to be bad, but if you think about what you are doing and take note of your form then no not really. Is it road or fell?
Also, descending hills on long days is probably more knackering than the uphill, so preparing your legs for descent is equally as important.
I've found squats etc to be beneficial for my climbing/descending. I'm not a big fan of doing millions of reps but learnt how to zercher squat to avoid trying to get a big weight over my shoulders without a squat rack. Alternatively 1 leg squats against a door frame are good.