I am in the financial field. I use Google search and Content network. As previously mentioned, I also bid lower for content nework than I would for Google search. I have a nice conversion with Content nework for my type of business. I guess, it all depends what you are selling. Give it a shot, it won't hurt any.
Google's search network seems to be very good. I did some testing with campaigns where I removed the search network and my conversion rates actually fell. IMO, the Google Search network is top notch.
Also, if you find a site in the Google Search Network where you don't want your ads to show you can request that your ads be removed.
On the other hand, Yahoo's search network is full of search arbitrage sites that you can't opt out of. I was the top bidder for our primary keyphrases and got sick of Yahoo's search network so I lowered my bids to start ranking 5th (not to show up in most arbitrage sites). My cost per conversion fell over 65% and the number of conversions I was getting only fell 10% or so.
In regards to the content network, in my vertical it's a total waste. I've even tested Content Network only campaigns (recently made available by Google) and even though I was able to closely control my bidding it was still worthless. When I played around with Site Targeting I saw a lot of sites suggested by Google based on their keyphrase suggestion tool that had nothing to do with my vertical. Based on this, I'm wondering if the Content Network is a little too broad with its contextual logic.
I have had a ton of success with Site Targeted campaigns though (after weeding through the crap). I was able to squeeze another 10-20% more conversions out of our Google account through Site Targeting.