The price has gone up considerably. For one block of keywords it went up from $35 to $80 this year. Also, they're very difficult to work with - continuously dropping stuff, decreasing exposure, etc. At least that's our experience with them.
I am only starting now (dec. 20th I went live) and I have $12,500 scheduled for the 3 month period, just under $15,000. I got the feeling when negociating that if I really wanted to push it I could have got in for maybe 9,000 or 10,000.
The thing is I am extremely happy with the results I am getting, the money coming in far exceeds the money going out, and even though it has only been 5 days, I am confident that I will try to get more traffic coming in for similar terms that I wasn't so sure about originally.
I experimented with keywords I thought might be off focus and low and behold, they are profitable as well. I think it is totally worth it if your landing page does the sale. If you're just sending traffic to a site hoping sales will come through you'd better have deep pockets, cause it can get expensive fast.