The next backlink advertising network I found was AdCaliber (http://www.adcaliber.com). I quickly read over their FAQ and was pleased to find that they promised permanent backlinks that only get removed when I choose. Other than that, system seemed similar to DigitalPoint although it was a bit more flexible in ad targeting. After creating an account, I received 100 credits which I could use to bid for backlinks. Apparently, AdCaliber works on a bidding system. You bid a monthly amount of credits to obtain links on certain sites. For example, I bid 50 credits to obtain links on sites with a Google Pagerank of at least 5 and Alexa Rank of at least 500,000. Then, when an open ad slot appeared on a site matching those qualifications, highest bidder would get link. In my case, I would be debited 50 credits per month. I was very impressed with system. I liked having ability to target my ads precisely. I was also impressed with ease of installation. With AdCaliber, you don't have to upload any files to your server. You just simply paste a short PHP code on your website. It was very simple. The only negative thing I have to say about AdCaliber is that it is much newer than DigitalPoint and its network is not as large, therefore not as many backlinks are available yet.

To sum it all up, DigitalPoint is a very effective backlink advertising network when you are looking to acquire backlinks quickly. I would not use DigitalPoint for long term SEO, though. AdCaliber seems to be your best bet for long term SEO and seems to give you better control over your backlinks.