The good people at Matica.com answered one of my prayers just recently by posting a tutorial on animating a balloon tied to a string. Interesting result.
I modeled this rabbit last year but, as with most things, hated it’s functionality. Finally today, I made a few changes to his rig and put him in a short animation holding a string with a red balloon tied to the other end. The animation simply serves to showcase the physics of the balloon and string, but if you find yourself falling in love with the rabbit, I don’t blame you. 
The steps for the balloon are incredibly simple – just model the entire thing in one mesh and apply a Cloth Modifier with gravity set to -1. Follow the tutorial for additional tips and tricks.
My animation was 300 frames, each rendering for about 10-11 seconds.
Happy Thanksgiving. :-)
Jonathan Williamson shows how to model a balloon and string, as well as an environment.
http://cgcookie.com/blender/2010/11/04/creating-a-bunch-of-balloons/
Matica.com shows how to animate the balloon and string.
http://www.matica.com/tutorials/blender/blender-simulating-a-balloon-tutorial
