I've been playing Team Fortress 2 since its public release in October 2007. Before that I played QuakeWorld TF and Q3F for many years also both of which were essentially free (you had to pay for Quake and Quake 3 but the TF mods were free). TF2 was the first TF variant that I paid for.
Steam tracks play time and over the last 5 years I've clocked up 2,500 hours. I bought TF2 as part of The Orange Box which I think cost about $20.
So I've long held this impression that TF2 is insanely good value for money in terms of cost per hour. Consider a movie is $20 and lasts 2 hours - $10/hour.
2,500 hours at $20? Not even 1c/hour!!! Except that's not the real figure.
On 30 September 2010 Valve released an in-game store called MannCo. There you can buy various virtual items including hats, paints (alternate colours for in-game items), gifts, and keys (for opening virtual crates that you randomly get in-game, pretty much a virtual instant scratchie). So keep in mind this store has been available for ~21 months.
Today I took a look at my Steam transactions and tallied up all my TF2 in-game transactions.
$750 Holy cow.
The largest transaction I can remember making was the $130 I donated as part of TF2's Japan Charity Bundle
Where did the other $620 go?!
One can buy a Pile o' Gifts which gives everyone on a server a gift (a random item). For many months I played almost exclusively on the games.on.net #02 server so it was nice to "pop" gifts there as I knew most of the regulars. Turns out I've used 11 of these suckers for a total value of $220.
And then there's the Secret Saxton ... for when you don't want to give everyone on the server a gift, just a random stranger :) I used $90 worth of these.
$130 + $220 + $90 = $440 out of $750 ... leaving $310.
Keys. As you play the game you randomly get crates. Crates contain various items, including the possibility of a rare hat. Rare hats means extremely low probability, I've never gotten one. To open a crate you need a $2.50 key. Turns out I'm more of an instant scratchie player than I thought -- roughly half of the $310 was spent on keys, and the remainder was miscellaneous hats, paints and tools.
So ... 2500 hours for $750 puts the real cost at roughly 30c/hour. Still good value but several magnitudes more than I was expecting.
And in reality the $750 was spent over the 22 months after the Mann Co. store opened so I've effectively been paying $34/month for a "free" game.
Now you know why TF2 is free to play. "Free" :)
PS: Do I regret spending so much? I am a little amazed at how much I have spent and I'm sure that if the total figure was regularly shown to me I'd curb my spending. However it's still a cheap form of entertainment, not to mention a helluva lot of fun, and I've met some awesome people because of TF2.