This article gives some useful explainations, even if that's before 4.3 came out:
If you’re going for the “pixel art” look then the camera’s
orthographic size is of critical importance; this is the trickiest
part of nailing 2D in Unity.
The orthographic size expresses how many world units are contained in
the top half of the camera projection. For example, if you set an
orthographic size of 5, then the vertical extents of the viewport will
contain exactly 10 units of world space. (The horizontal extents are
dependent on the display aspect ratio.)
Recall that your sprite quad is 1 unit to a side. That means the
orthographic size tells you how many sprites you can stack vertically
in the viewport (divided by 2).
To render the pixel-art look cleanly, you need to ensure that each
pixel of the sprite’s source texture maps 1:1 to the viewport display.
You don’t want source pixels being skipped or doubled-up, or your
sprites will look distorted and “dirty”. The trick to ensuring this
1:1 ratio is to set an orthographic size that matches your vertical
screen resolution divided by the pixel height of a sprite.
Let’s say you’re running at 960x640, and you’re using 64x64 sprites.
Dividing the vertical screen resolution (640) by the pixel height of a
sprite (64) yields 10, the number of 64x64 sprites that can be
vertically stacked in 640 pixels. Remember that the orthographic size
is a half-height, so your target orthographic size in this case is
going to be 5 (one-half of 10). It should look like this:
If you set your orthographic size to half or double that target you
may still get usable results, because the sprite’s vertical size will
still divide evenly into the viewport’s vertical size. But if you set
the orthographic size incorrectly, you will see some pixels skipped or
doubled, and it will look very bad indeed:
You don’t need to be confined to a single, fixed resolution in order
to render clean pixel art. The simplest way to handle variable
resolutions is to attach a custom script to your camera which sets the
orthographic size according to the current vertical resolution and a
known (fixed) sprite size:
// set the camera to the correct orthographic size
// (so scene pixels are 1:1)
s_baseOrthographicSize = Screen.height / 64.0f / 2.0f;
Camera.main.orthographicSize = s_baseOrthographicSize;
While that is a simple fix, it does have a drawback: as the screen resolution
decreases, you’ll see less and less of the world, and sprites will
take up more and more of the screen. That’s the consequence of keeping
a 1:1 ratio between source and screen pixels: a 64x64 sprite takes up
more apparent space at 640x480 than it does at 1920x1200. Whether this
is a problem or not depends on the needs of your specific game.
If you want your sprites to remain the same apparent size regardless
of screen resolution, then simply set the orthographic size to a fixed
value and leave it there regardless of the screen resolution. The
drawback there is that your sprites will no longer have a 1:1
source-to-screen pixel ratio. You can mitigate the ill effects of that
by only allowing resolutions which are exactly half or exactly double
your target resolution.
(some emphasis added)
This obviously works better if the height resolution is divisible by the sprite size, but even when it isn't, it still gives a good approximation of a decent result.
cameraSelf.orthographicSize = screenH / (float)spriteSize / 2f;