Behind our sink, because there's a window, our horizontal outlets are just above counter height. In other places they are just below the upper cabs, so finish at 54" above the floor. That way they are mostly out of sight and don't interfere with the backsplashes too much, while still being handy to use.

You can barely see the outlet in this picture. Look at the black object sitting on the left end of the windowsill...It is plugged in just below it, where you can see another black object just to the left of the aluminum compost bucket.

I'd always intended to paint the outlets on this wall burgundy, so that they blend better. Maybe someday...

A closeup of one on the rangetop wall (after the tile was grouted, the outlets blend better than it does in this photo):

I have them, and love them. They're just above the counter, so most of them are hidden away, but very convenient to get to. The bottom is less than an inch above the counter.

You can just see three of them in the corner by the mixer:

Oh, why didn't I think of that? They look great installed horizontally.

Plan your tile layout and you can even get the outlet to line up with whole tiles on the backsplash. We actually ran the wires first, kept them long, and put the boxes in exact position once the tile started going up. Its an extra step, but worth it.

I had mine installed right under the top cabinets. I don't have counter or upper cabs yet and haven't used them but I know it will be better than what I had before!

I did this (fit 'em right into my subway tiles) and love it. They get totally hidden by the appliance using them. Did my own tiling, so it was easier to place the receptacles exactly where I wanted them, but you can do this for your electrician in advance with some very careful measuring and a sharpie. The first shot's not great, but it shows how I actually went and laid out my tile courses on the wall prior to putting the electric in.

*martini obligatory for all DIY projects

Palimpsest is right. If you know well in advance what your tile will be take the time to calculate it out carefully and you can work in the horizontal outlet to fit inconspicuously with the tile.

She also has a great idea by setting up a flexible positioning of the outlet connections, but you might not be able to get away with it. Your city code may require the outlet boxes to be fully installed before the wallboard goes in. Find out ahead of time. Ours does. The electrical inspector would not have allowed us to wing it after the fact.

In our community, code says outlets need to be positioned every 4 feet around the perimeter of the countertops in new construction areas. Also, a dedicated circuit for a microwave needs to be included and must have a GFI outlet. DH was the electrician, not a professional. We had to think through all our appliances and the positions for the outlets at a time when I was hardly ready to think about it. AARGH! Now, we have to live with our previous decisions. Generally, I think they were good ones, but....we'll see.

Remember to tell electrician if you want white or cream-color outlet parts. Same with light switches. My hubby doesn't notice this kind of thing and unless I remind him, he would put both together in one installation. If you are planning to have light switches in the same place as outlets, be sure to discuss with installer the potential for dimmer switches too.

Don't forget outlets for ...
undercounter t.v. or radio or coffee maker or whatever
chargers for phones
laptop computer
electric knife
vacuum cleaner

Do a brainstorm. Add to my list...vacuum sealing machine, crockpot, electric skillet/countertop broiler-oven, large coffee pot that can blow fuses, dehydrator, toaster, iron, chargers for appliances that haven't been invented yet. I now wish I'd put an outlet under the countertop on the end of my peninsula; I thought one at the floor was sufficient, but there's a difference between vacuum cord and iron cord position and usage. Also, when you get old, having an outlet close at hand trumps bending, even for appliances like a vacuum cleaner. --Florantha