but I had a pretty busy week. "Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization" (from the package insert). However the primary mechanism of action by far is the last of these (improving insulin sensitivity), which is why it is used in type I as well as type II diabetes. Perhaps I oversimplified, but the OP seemed not to be looking for complexity.

By the way, I love wikipedia, but it is often quite wrong about prescription drugs (not too far off this time, though). Try drugs.com or drugdigest.org - both are free and have good info. Wikipedia is just too vulnerable to armchair experts to be a good medical resource.