Hmmm, interesting thread. I never really thought about it until now.
Since I've spent about $7,000 on music alone, and have about 600 paid apps at all price ranges (in addition to countless movies, rentals and season passes), I am sure that I am close to the $10,000 mark now (since the iTunes store opened).
According to my financial application where all my transactions are stored, I've spent $1,800 in the last 12 months on iTunes media (not counting the gift cards I normally receive throughout the year).