Apple has quietly updated the design of 85-watt MagSafe power adapter used with the 15-inch and 17-inch MacBook Pros. The new connector design features an aluminum tip instead of the plastic one which is still available on the 60-watt MagSafe power adapters [Ed. note: this link is now broken, sorry for the inconvenience] used for 13-inch MacBook Pros and MacBooks.
Beyond the aesthetic redesign, there doesn't appear to be any added features. The new 85-watt MagSafe now mimics the form of the 45-watt MagSafe power adapter used by the MacBook Air. The advantage the 45-watt and new 85-watt MagSafe power adapters have over the existing 60-watt version is that the design allows for a more slimline interface while connected to the MacBooks they power.
Thanks to reader Max M. for the tip.