What are the various availiable types of Cabal Government, and what, if any, is the difference between them

Tacos speed up your out-of-combat health regeneration, but beyond that there are no other effects known at the current time. (The health regeneration bonus is actually pretty noticeable, even considering how quickly you regen in this game).

You can disassemble them into nachos, but there appears to be no use for those right now.

And of course they're delicious!

EDIT: Apparently this achievement just rewards a paltry amount of XP and nothing else.

DOUBLEEDIT: As of issue #2:

The coveted Taco Hat is now available if you have consumed 7460 tacos or more in-game.

This is actually confusing but I did a little googling and found this dev blog from the lead designer. I have added emphasis to the key parts of the paragraph.

In order to explain the progression we need to start talking about xp. At the bottom of the screen is the xp bar, and when the player has filled up 1/3 of it they will be given an ability point. Filling out the whole bar gives a skill point. A player gets xp from many different sources: Killing monsters, PvP, missions and crafting. The amount of xp needed to get an ability point or a skill point is static.

So it looks like everyone was on the right-ish track but I think we were reading too much into the bar.

EDIT: A bit more info from playing more tonight. The blue area will fill up each third of the XP bar as your progress. When you completely fill the bar you will get an AP point and the redish tint will go over that section of the bar. When you fill all three bars, that is when you get an SP.