Howdy,
Hmm...for me it would be 500k miles. That represents a trip in F to Europe for the family - so I'd use it.
I don't bank my miles. I use them now - I love to travel with my family and can take time off to do it when I have the miles.
I can't imagine that my balance would ever hit 1MM - although it's possible.
I guess I'd worry they would end the program or up the requirements or something. Free trips now = more money to save/invest - so in the future I'll have more money to travel
Just my two cents.
Keep the faith,
Pakse