This is probably one of the most important / useful feature in any image editing software - any knows how to draw curved line in Pixelmator?
The best you can do in Pixelmator 1 is arcs using the oval selection tool. Select an area with the selection tool set to the circle/oval setting and then trace the selection (Edit -> Stroke) on a new layer. Once traced, erase the part of the trace you don't need. Reposition, stretch and mangle with the layer tools.
Update: Pixelmator 2 was released via the App Store today and the pen tool lets you draw and manipulate curves now. Works great.
Pixelmator (1.x) is a raster-based image processing software and doesn't support curved line and other vector functions.
Edit: It seems that the next version will have some vector tools: http://www.pixelmator.com/sneak-preview/