While not miles, I lost 127,000 Starwood points.
This was partially due to some health issues that kept me from traveling for b6 months.
My fault, but was given no "mercy" from SPG. I switched vto HH since.
A number of times I lost out on Delta vouchers,usually for small amounts. Once, I lost over $400 by mistaking the dates I had to use them by.
Wow, this thread is really depressing.