8-22-10: 57,012 miles - The car came with no rear seat belts, but has a surprisingly roomy rear seat for such a tiny thing.  I purchased a universal clip seat belt from Advance Auto Parts and installed it without the lap belt, just putting the brackets in.  I then purchased a Safety 1st Alpha Omega child seat - the key was that the furthest back part of the seat is only 11" wide - this seat has a very narrow rear and widens towards the front.  Its also upright so that we don't have lean issues and it doesn't jut too far forward.  I secured the latch clips to the empty seat belt brackets, and secured the rear latch to the right seat belt bracket.  I put a few towels behind it for extra tightness, and then tightened it - a very easy, safe, cost effective alternative to a $400+ Porsche OEM child seat.  My kid loves riding in the 911.