In the last five years I've managed to earn and spend about 1.5 million miles and points, with maybe 50k airline miles from actual flying and ~400k points from actual Hilton stays. Between churning, manufactured spend and promotions I'm able to do 1-2 international trips a year in first class, staying at good hotels. I mostly travel to Asia and get great value out of free flights on Singapore, Cathay Pacific and Japan Airlines.
It's an awesome hobby if you: a) have time to kill b) are single and c) have an insanely flexible schedule.
I used US and BA miles earlier this year to fly to Malaysia and Thailand for free (well, plus taxes) in first class, spending five weeks between Hong Kong, Penang, Koh Lanta, Beijing and Tokyo.
Drinking $300 champagne at 35,000 feet on a flight you didn't pay for is a rather fun feeling...