The paid version offers you up to 50,000 links per day, the autolicious plugin for autoblogs which will index every post for you as it's added to your blog, plus the ability to make RSS feeds out of only 5 urls. It has 3rd part compatibility with several link building companies, great customer service, and even makes you a cappuccino. (ok it doesn't do that last bit...) Anyway, point being, it's worth it if you want to really see your links working for you. The way I see it, you're saving money by getting the links you've made indexed properly, rather than having to build four times as many....