We know it's reverse engineering, but it's a feature that is crucial.

We need to be able to resize and rotate individual layers

Like it's in GIMP. Open gif's and see the layers, save as a animation (gif)

8-bit PNGs with alpha transparency are images that can contain semi transparent pixels, unlike regular 8-bit PNGs. The main advantages over 32-bit PNGs is that they take up less space, and degrade more gracefully with IE6.
Few editing tools support them, for some reason.

More info:
http://blogs.sitepoint.com/png8-the-clear-winner/
http://www.communitymx.com/content/article.cfm?cid=E4024

This will let you more easily select a wide range of colors instead of having to mess with the palette size.

Exactly like described here:
http://blog.getpaint.net/2012/04/08/new-features-for-paint-net-4-0/ in the "Antialiased Selections" part. Would be awesome!!

being able to open paint.net files and psd files in Pinta would be extremely useful

when you use the tool line you can bend it in several places

As in Paint.NET, by moving mouse while holding right mouse button.

Add printing option to Pinta like File | Print.
More info at bug tracker: https://bugs.launchpad.net/pinta/+bug/728426

Add ability to use pressure information from Wacom tablet pen.
Useful for Wacom graphic tablets and TabletPCs.

The first thing I missed within seconds of using ver 1.1 was that I could not adjust the size of the content inside the selected area as I often do after pasting a cut image from an external source. This is one of my most frequently used features in Paint.NET The Move Selected Pixels Mode should have handles to allow resizing of the selection and its contents before pasting.

On statusbar: Images width, height, colors and width, height for selection.

When selecting gradient a second option to use transparency mode is available to allow gradient from solid colour to transparent. Really usefull tool from Paint.Net