Illustrator is similar enough to Photoshop so that there's not a BIG learning curve, but you have to learn a whole new way of creating, as Illustrator is not pixel based like Photoshop but is made up of lines, basically. Think of it as making everything in Photoshop with a pen tool and you'd be close to Illustrator. The advantage is that you can make it any size from postage stamp to billboard with no loss of quality. Takes a while to get the knack though, but some cool stuff can be made.