So I've screwed around with Xooxer's Platformer Test Source and I've been pulling the code apart to see what its capable of. If you haven't seen it yet, its side scrolling pixel movement in all it goodness, check it out here:

When I first saw it, I thought it looked absolutely fantastic. However, I've found multiple problems after stacking different types of objs and turfs on top of each other and checking the collision system. The BIGGEST problem is the fact that arc2tan() seems to cause a majority of problems. Since I'm not exactly the best programmer in the world, let alone with BYOND, I don't know exactly what to do.

So, anyone that wants to help or just to take a look at it, jump on in, its fun to mess with regardless. If you do find a fix, remember to tell everyone (especially me).

The only problem I ever noticed was that Xooxer never disabled the default macros, so you could move and ignore collision, gravity, etc., though your actual pixel location wouldn't change. Setting client.control_freak to 1 is a solution to this.
In response to Jeff8500
Uh... not a good one, though. The overall best one would to just eliminate the ability to move that way, not to remove the ability to attempt to via macros. All the default movement commands go to client/*Direction*() and then client/Move(), so they're easily disabled.
In response to Kaioken
It still works pretty well while leaving normal movement functional, if you want it. If you don't want to allow normal movement at all, though, yeah, you're right.