I'm adding receptacle circuits to an older kitchen with ceramic tile on the walls above the countertop. The tiles measure 2"x5/8" and the grout is very thin, 1/16" or so.

I don't imagine that cutting an outline of a Carlon old work box with the tiles in place will be too successful. I'm thinking that what I will do is:
Mark an outline of a 1 gang owb on the wall.
Figure on removing all tiles that reside inside the outline. Even if a small portion of a tile is within the outline, the tile will come out. (So, even before the hole is cut in the plaster beneath the tile, a much larger "hole" is made in the tile pattern.)
Scratch out the grout between affected tiles with a broken hacksaw blade.
Work the tiles out.
Cut hole for owb, insert cable(s), set owb in wall, flush with tile.
Reassemble and set tiles, cutting as needed and grout.
Anchor and wire box.
Labor intensive but I think in the end the product will look good.
Whad'ya think?