The +Pack has two very useful components for the Glif: One is the Ligature and the other is the Serif.
The Ligature screws into the Glif. You then put it on your key ring. Quite convenient if you take your Glif everywhere along with your iPhone 4 or 4S. If I could change two things on the Ligature it would be: Add a swivel, and a brass option. Compared to car keys and fobs the Glif is big, especially when the long end is sticking out. A swivel would help keep the long end down. The brass option matches well with the original batch of Glifs that had brass tripod screw threads. The Ligature is an ingenious idea that keeps things simple by making use of what is already there to add a convenient feature.
The Serif perpendicularly connects to the Glif and secures the iPhone 4 or 4S; now it has zero chance of falling out. At times I would put the iPhone in portrait orientation on the Glif, but I always felt it was insecure: The iPhone is off to the side and the vertical grip is too short to keep it secured. The Serif thoroughly eliminates any insecurities and gives me the freedom to use the iPhone on a tripod any which way I want.
The Glif is a small, simple tripod mount and stand for the iPhone 4/4S. The Ligature really secures the iPhone/Glif and the Serif connects the Glif to your key chain making it convenient to take it everywhere. An extra feature: The Ligature fits neatly inside the Glif. Tom and Dan has done it again: Simple, easy-to-use, must-have iPhone tools that add convenience without adding complexity. At US$12 the +Pack is a great deal. Make sure to pick one up at Studio Neat.