Same here, Rudi taught me that trick in the 90's. Up until that time I would save the miles for a free business class ticket, but he pointed out that buying a cheap coach ticket and using miles to upgrade resulted in the flight earning miles and counting for elite status (and the miles counted toward Million Miler status as well). It also allowed you to fly in business more often.

These days, though, as was mentioned elsewhere in this thread, the miles cost for upgrades has greatly increased (particularly for the discounted coach tickets) or requires a cash co-pay, if miles can even be used to upgrade (some fares are not eligible for upgrade no matter how many miles you offer). So, I don't upgrade internationally with miles as much as I used to, although I still do so occasionally.

My largest outlay of miles is once a year my S.O. and I will take an international vacation in business or first to some exotic place. Using miles for such tickets is the best "cents per mile" redemption, and certainly helps V's mood.

I also occasionally use my miles to get tickets for vacation visits by relatives and friends, and once or twice have used them to get last-minute tickets for myself where the cost of buying the ticket would have been outrageous.