How many layers do you usually use for a 6 inch cake?  They always look so tall.

i use 3-4--

it's a matter of proportion--in a 6 x 8 x 10 x 12--all 4 inches tall--the 6" cake is 2/3 as tall as it is wide--the 12" is only 1/3 as tall as it is wide--makes a difference visually--but i often like for my tiers to diminish in height the smaller they get--sometimes I use an inch high dummy for the bottom tier to sit on and i ice it all together as one tier so i can get it tall enough --

just depends on the cake

I prefere to use 1 1/2" two inch layers so the resulting cake is 6X3.  I think this looks much better.

A4-6 1/2 inch layers, depending if it's stacked or a stand alone cake, and depending on the style in going for. I never make a cake under 4" high, unless I'm going for contrast in a tiered cake.

I very often will have my 6" cakes 5-7 " tall.  I like the look of the taller cakes.  The top tier in my avatar is a 6x7. 

..........I prefere to use 1 1/2" two inch layers so the resulting cake is 6X3.  I think this looks much better........

I should have mentioned that is what I prefere when using a 6"er for the top tier of a tiered cake.

If it were a stand alone, then I can see making them taller.  And, of course when used for a perticular look within a multi tiered arrangement.