The burnt taste is from residue on the heating coil.
I took a few attys apart and they consist of 2 copper wires poking through a circular ceramic plate which holds the weld between the copper wires and a heating coil all wrapped in a sort of "foil" that feels a little like miniature brillo pads. I am not sure what type of metal the coil itself is made of but it's definitely not copper (a glowing heated copper coil will emit gases which you probably don't want in your lungs). When you look into your atty you are seeing a metal arch that snaps into place around the ceramic plate and is also wrapped in this metallic meshy brillo type stuff. Inserted under this little metal arch is some sort of fibrous material, I assume it is there to hold the liquid, but I remove these because it contributes to bad taste and besides I have no idea what its made of and I don't want whatever fumes it is burning going into my lungs because almost all these "fibers" I removed were half burnt (you can remove them by gently poking a toothpick under the little metal arch and twisting it around to get the fibers out, or by removing the metal sleeve around the atomizer and poking them out).
It's a pretty simple design (in fact it's the exact same design as a light bulb, but without the bulb), but it makes me wonder if the ceramic or the coil itself is giving off any sort of fumes I should be worried about. There is no doubt in my mind that there are better (and safer) ways to boil liquid than exposing it directly to a metal coil.
By the way, if you want to take one apart yourself, the gold part is jammed into the metal sleeve (not screwed). I used two pairs of pliers and just pulled it right out (some of them need a good twist or two to come out), but you will still have the ceramic plate stuck inside the sleeve so be careful or you will break the wires. You can simply poke a toothpick or something else in there to push out the ceramic plate (wrapped in that wire mesh stuff I mentioned earlier).
As far as cleaning, I don't think there is a hell of a lot you can do about residue on the coil, since the coil is made from a very thin tiny wire and pretty much everything that can clean residue from metal is probably going to leave chemicals in there that will KILL YOU if inhaled a lot. I would guess the only real option is to use clean juice that doesn't leave much residue when it is boiled into vapor. I would imagine some of you guys who sell juice could use that as a selling point.