I searched these links for improving skill in using Illustrator. Some people mainly use photoshop to create their own products and they rarely use Illustrator. I hope those link below will help. It gathers a lot of tips, tutorials and many things else for this software.

http://www.vtc.com/products/Adobe-Illustrator-CS3-Tutorials.htm

http://www.tutorialized.com/tutorials/Illustrator/1