Lenovo is updating the design of its ThinkPad laptops to keep them up-to-date in a market where computers are getting thinner and lighter at a fast rate. The ThinkPad's external appearance isn't changing a great deal, but it is getting considerably thinner and lighter. The changes are exemplified in the new ThinkPad T431s, which will go on sale next month for $949 in the U.S. and some other countries.