I have a pair of crash pads shorts - haven't tried them under my MX pants yet, but I've used them for racing DH and they work fine. My only complaint is that they feel a little bulky, depending on what I'm wearing them with. No problems with durability, but I haven't worn them that much, so it doesn't mean anything at this point.
I have the Azonic Z-5 body armor jacket - which I absolutely love. I use it both when I'm on my motorcycle and on my DH bike. Comfortable, ventilates well, and has held up to an unfortunate amount of wrecking. ;)
Definitely has prevented a lot of scrapes and bruises for me. The only thing I had to figure out was to keep the straps on the elbow guards tight enough so it doesn't slide around - when I left them loose, the mesh underneath ended up scraping my skin in a fall. But since I've tightened everything properly, I've been scratch free. (Wish I could say that's because I've been crash-free, but that's not the case!)