This is happening to me for a while now, and is extremely annoying since I need to create logos and other graphics for web use.
I am going to explain through steps what is going on, please see below and in attached pictures and pixelmator file.
I create a new file of 518x140 pixels with 150 pixels/cm.
I write some text, whatever, it does not matter the font.
I see the file in the pixelmator window at 100% at it is smaller in size compared to the actual exported file. See one of the pictures attached where you see both files next to each other.
To see the actual exported file I need to zoom the file at 200%.
It's like Pixelmator is exporting files zoomed at 200% but with same overall size and resolution.
I open the file after exporting jpg at best quality and the lines are blurry, you can see the pixelated edges of letters, kind of very ugly.
The bigger files is the size that the file opens on my computer and also how web browsers see it.
Please fix this as soon as you can ... or I don't see how I can use your application anymore. I saw others complaining about this in other posts too, from different points of view, but the problem is zoom and blurry pictures. If you look closely at the file you see the jagged edges.
I use latest Pixelmator version on latest Mac OS version.