The new MBPs have a differently-designed connector for their MagSafe than the older ones (2007-2008 or so). However, not only are these electrically equivalent, the actual physical end of the cable is compatible; the difference is just in how the cable connects to that connector. So if you have an old 85W brick, you can use it with the new MBP, so far as I can tell.
DISCLAIMER: This information is worth about what you paid for it. The only macbook for which I take any responsibility for damage as a result of this information is my own (which is currently plugged into my old 85W brick from 2007).
DISCLAIMER: This information is worth about what you paid for it. The only macbook for which I take any responsibility for damage as a result of this information is my own (which is currently plugged into my old 85W brick from 2007).