Where can I get some GIMP tutorials?
There's always YouTube .
The GIMP User Group has some as well: http://gug.criticalhit.dk/viewforum.php?f=4&sid=4a4ed54fbecb7a9f84e1bb53c8f78bda
I found "grokking-the-gimp" very helpful as an all inclusive learning tool and reference. You can install it as a package from the Ubuntu repositories. For the most part, the online tutorials are task versus application function oriented like Grokking the GIMP, which can make them superior if they cover the task you which to accomplish. Both have their place.
http://www.giesdesign.com/ is an italian blog with great and simple Gimp tutorials.
If you want to learn a bit more about image processing (particularly photographic retouching), you can head on over to my GIMP tutorials (there's a couple of basic ones, and a few that are a little more advanced):