Here is a cool infographic on numeric domain names from Giuseppe Graziano of GGRG.com. GGRG is a domain brokerage that specializes in short letter and number domains. Their expertise in the short domain niche has led them to create this infographic which gives an overview of why numeric domains are so valuable, predominately in the Chinese market. In China, every number carries a meaning, and some numbers are luckier than others. In recent times, the value of short numeric domains have gone up significantly largely due to the Chinese market.
Click on the infographic to open a new window. Then click on the image again to view the infographic in full size.
Guiseppe wrote a definitive guide on numerics here.