Regenerating icon files
The Connectr menu bar icon is saved in Gimp's XCF format, as connectr.xcf.
The OS X icons are generated from the XCF by resizing it down to 80px with a 300 DPI and saving it as a PNG, connectr_80px_300dpi.png. OS X does actually use the DPI, so setting it is critical to getting sharp rendering at the right size on Retina displays. The menu bar itself is 22px high, so a 20px @ 72dpi icon looks ideal. To handle Retina displays, this means bumping to 40px @ 150dpi. However, you can keep doubling, and I find 80px @ 300dpi to be nicer to work with, so I went with that.
The Windows icon is generated from the OS X PNG, mostly because Gimp is an idiot and doesn't like exporting XCF->ICO directly. Just open connectr_80px_300dpi.png and export it as connectr.ico without any changes.