I'm in the process of building my second set. Nothing really "wrong" with the first one, just wished I had thought through the lay-out and ease of use a bit more. The big lesson learned for us was wishing we'd have bit the bullet the first time and purchased drawer slides. This time I bought the 5' slides, rated at 500 lbs off amazon. Confirming the order physically hurt, but will be a better system for what we use it for than not having drawer slides at all like the previous version. I just put down some HDPE for the drawers to slide on, which worked, but if I got too much stashed in the drawer I'd about give myself a hernia pulling them out. Wifey also hated pulling the drawers out... which was the push to rebuild.
Also including a cubby at the front (6'4" bed, with 5' drawers) which is great storage for the stuff you don't need for everyday use, but still want to have tucked along. I keep my chainsaw/gas/bar oil up there, tow straps, tire puncture kit, etc. up there. Time and money depending, I may stash another 12v in there, with a solar panel on the roof. Hook up an inverter and it would be used for lights and charging electrical stuff.
Another lesson learned is this time I'm building it all out of HDO plywood, meant for concrete forms. More plies to the plywood, with better glue, meant for repeated exposure to wet concrete, hopefully mean they'll last longer. My old set-up wasn't necessarily broken, but spills, weather, and hard use were starting to take a toll. Also, I'm using a Kreg Pocket Screw system to put everything together this time. I glued and face screwed my last one, which split some plywood out, and meant I couldn't remove it without completely demolishing the top and bottom.
Any other questions?