I'm curious about how you divide your various action categories amongst input devices/methods.
One of my teams includes a Tankadin and a Priest.

I actively play the Pally, because positioning is so important, and have my Priest as a drone. I use QWEASD to move my pally around (in conjunction with the mouse of course).

I use the arrow keys and a couple of KP keys on those rare occasions that I need to move the Priest around in some fashion other than just /follow. That's mostly just getting out of a blob of fire or something though. Typically, once he's in place he just stays there.

I have three sets of Priest healing macros:

- One for the FOCUS target (who is usually my Pally)

- One for the MOUSEOVER target (I have a trackball dedicated to the Priest machine so I can position the pointer over a (very large - three cheers for X-Perl!!) health bar without fear of moving it when I throw my mouse around the desk in a fit of Pally action!)

- One for the TARGET, which goes to my target's target if my target is hostile (i.e. if I target a mob, my heals go to whoever has aggro).

It so happens that I currently use an X-Keys stick for tanking and an X-Keys Pro for healing, but since tanking is a 4 button affair right now (one cast sequence, one hammer, one consecrate, one to BoP my target's target), that's over-kill.

The healing macros would lend themselves well to G-Key macros, but I've had mixed experience with my G-Keys - sometimes they work, sometimes they don't - so have completely stopped relying on them.

In your terms, then, I have:

- Character A's Movement on keyboard 1
- Character A's Skill-use on keyboard 1
- Character A's Mouse cursor on mouse 1

- Character B's Movement on keyboard 1, broadcast to machine 2.
- Character B's Skill-use on an X-Keys Pro.
- Character B's Mouse Cursor on mouse 2, which happens to be a trackball.

What will distract you most isn't healing, but removing magic / disease. I use a (very large - three cheers for SmartDebuff!) SmartDebuff window for that, which means I just need to roll the trackball and left or right click in the right place, but it's still a distraction.

I suspect the reason you don't see much about two-boxing is because there's not really much for you to do with just two characters together.

Personally though, I see no reason at all why you couldn't successfully play two characters in a PuG.

Assuming you're on the ball with both, the only give-away will be that your Priest follows the pally in a very suspicious fashion when you're moving between encounters

Some encounters outside of 5 man instances need a great deal of mobility, which you may not be able to do effectively, but Heroics? Sure. Why not.