If you were to ask me which of the Adobe products was the hardest to learn, I'd have to answer Illlustrator. If you asked me which of the Adobe products I've had the most fun with, I'd have to say Illustrator!
That may be in part to the freedom that Illustrator gives you to be a "real" artist. I can sit down with my Wacom Tablet and just draw naturally. I love it.
Creating stunning illustrations, though time consuming is tons of fun. My favorite trick? I love to use illustrator for text that I want to blow up. I create my text box, choose type>create outlines and now I have a vector version of my text that can be blown out of proportion or used in tandem with other programs to create awesome posters and really fun effects.
When I was first learning Illustrator I came across a remarkable book by Scott Kelby, Illustrator Killer Tips. He's actually recently put this book on sale. It's a remarkable resource. Start having fun!