Is there a way to determine how many hours you have been playing World of Warcraft?

For your individual character playtime just type /played whenever you are logged in. There are also a couple of addons available that do this every time you log in with a character and give you a nice overview (I believe "Altoholic" was one of them - can't check right now).

Yup! /played will tell you (on each character) how many hours you have logged!

Some addons (Carbonite for one) will add up all the times on all the characters you've played on, so you get one big number.

What it won't do is multiply that by your hourly wage to see how much money you lost playing it. For me, I'm in the hundreds of thousands lost...