If the pen tool is Illustrator 101, then the Gradient Mesh tool is the advanced, 400-level course. Gradient Mesh is the preferred method for photorealistic illustration today- it’s the airbrush for the new millenium. If you haven’t seen any of the many mind-boggling examples of what the mesh tool can acheive, you really need to check them out.
But the tool shouldn’t be intimidating to those with bezier curve experience. For one thing, it doesn’t have a steep learning curve like the pen tool. It’s like Othello: a minute to learn, and a lifetime to master. The basics really are basic, and it demands more patience than skill to produce solid mesh work. But that’s not to say there aren’t tricks out there.
There aren’t too many tutorials out there, but I have found one worth sharing. It comes with a completed .ai file and a helpful step-by-step that includes some great pointers. Among them:

• Cmd+Y to toggle outline/preview modes. If you didn’t already use it, you will now.
• Use a template layer. Then you can mesh in outline mode- while viewing the template in preview mode!
• Now that you’ve got the outline-over-template groove going, use the eyedropper to add color. Eyedropper from a photo? In Illustrator? Yes, double click on the eyedropper in the toolbar & uncheck “Appearance.” Piece of cake.
• Work with layers. This is the author’s preference, but I trust her! It keeps things organized, and you can easily blend the edges together later on.
• Keep it simple! As with the pen tool, conserve points.
• If you forgot the last tip, Opt+Del deletes a mesh point.
• Add points for lights & darks, not midtones. The mesh takes care of those.
That’s it! Read the tutorial and start meshing around!