They work very well for me. Been with Kontera for almost 2 years now, I use them for my health site and the revenue is almost as high as Adsense.
I use to have them but have to remove them. One of the reason is the low pay but well I guess kontera might work with other sites and also I just find contextual link spammy.
I used to have Kontera ads on my entertainment websites, but months ago I completely removed their ads, because it was a complete waste of ad space on my sites. I believe Kontera will pay you low on all content of the site. Try using some different ad network if you have other choices.
I use Kontera as one of my networks and it's 5% of my income. Nothing to be excited about but I run it alongside other networks just fine.
john3003- Do you have US traffic? It matters a lot because US traffic earns a lot more with most ad networks. If your traffic is international then you probably aren't making that much.