Short and simple reply, maybe...

- Is wall washing the cabinets this way common; i.e. using an angled
(adjustable) trim (at 30 deg)? Is there a better way? Will a wall wash
trim do the job better than a retractable eyeball, gimbal, etc.?

+This much detail is only common when somebody gets bitten by the
"lighting bug."
Wall washers will definitely do a better job, and not hang down below
the ceiling! That is exactly what they are designed for. The Prescolite
LVH4-LV6 is my favorite. See
http://www.prescolite.com/product/Productsweb.nsf/0/41F168205DE0285E85256B29007B22DD/$FILE/ARCH-INC-006_LVH4.pdf?OpenElement

- I'm considering 3" line voltage cans (with GU10s) (new
construction) or low voltage cans with individual transformers
(remodeling) probably with 35W-50W MR16s. If I use halogen at about
15"-20" from the cabinet surface, will the heat cause any problems? Any

cooler halogens (does dichroic coating make it cooler - not the light
but the heat coming from the lamp)?

+ The dichroic coating lets most of the infrared energy go out the back
of the bulb. This keeps the beam cooler.

- if I install regular downlights (not at an angle) pointing toward the

edge of the counter (24" from the wall, 12" from the wall cabinet
surface), will it have the same "wall wash" effect? (Actually when I
tried it, it didn't look like the same as pointing directly at the
cabinet surface, but I might be mistaken.)

+ What you saw is what you would get. You might also want to look at
the various lenses and shades for MR16s. They are wonderful when you
want to fine tune the beam shape, smoothness, glare or even color. They
fit with or instead of the glass cover over the lamp. See the
manufacturers accessories and then know that there are more!

- I'm planning to use 1 can for each door (they are 16-18" wide). Is
this too much?

+Some would say yes other no. It is a lot depending on your final
selection of lamp. It is also somewhat expensive. As Rodger noted the
PAR lamps are far cheaper and simpler, but they are not as effective or
flexible. All professional lighting designers prefer MR16s (or very
similar) for detail controlled light.

Good Luck
Richard Reid, LC
Luminous Views
www.luminousviews.com