I only use tracking because of eBay/PayPal's policies, and because I got burned enough. I also have recently stopped shipping to any foreign nation that does not have tracking (I lost $50 on a shipment to Saudi Arabia that cleared Customs but lacked a delivery record).

In addition, if you do not use Tracking, you do not qualify for the discounts on fees offered to Top Sellers, since on-time mailing is part of the equation.

For the record, I have never had anyone who reported non-delivery later contact me to say they received their package later.