Version 0.10 of the user manual for GIMP 2.2 has now been made available to download from ftp.gimp.org and includes the following improvements.

How a longtime Photoshop user adapted to GIMP by rearranging toolbars, customizing keyboard shortcuts, and more.

Although GIMP does not include a diamond texture option, as of June 2012, experiment with digital patterns, paint brushes and filters to superimpose a sparkling effect.