I have an Otterbox on my Droid 4 and after some minor modification, my phone fits like a glove in the lapdock at the back without having to take the case off.
(I actually have the Atrix lapdock but they are essentially identical. Actually, I think the Atrix dock is about $20-$30 cheaper, at least where I am; I got it brand new from bensoutlet.com for $60 shipped.)
First, I used a razor to trim off the annoying silicon flap from the Otterbox that covers the USB and HDMI ports.
I removed the cover for the docking interface and slightly bored out the two holes for the USB and HDMI male ends before reversing them so that the phone will mount properly. In order to make them reach out far enough to dock the phone on with the case still on it, I wedged a few slices of a white gum eraser that I cut to fit behind the cable ends so that they stick out about 3/4 of an inch; plenty of room now to slide the phone on while it is in the Otterbox and the newly extended jacks are super solid without any wiggle room at all. It actually feels sturdier than it did before when mounting it without a case on as I find that the bulk of the case helps to fill out the platform the phone docks on.
Now that the two male ends of the USB and HDMI connections stick out slightly further than they used to, I had to get creative in order for the flip-down docking pad to properly close. Took me 5 more minutes to Dremel out two small openings that would allow for the dock to shut, and now it works perfectly.
It's true that the touchpad isn't multitouch, but I use a Bluetooth mouse 99% of the time anyways so it doesn't really impact how much I love this thing. For $60, you can't go wrong!
I'll post some pictures of it shortly, I'm out now and don't have it handy. I'm pretty amazed at how easy it was to do, and it doesn't look like a hack-job at all.