First, for the link builder, the obvious. You post a URL in the “Share What’s New” box, below and share it with “Public”, or with one or more of your Circles. You’ve now technically “built links”, because those URLs will appear on the timeline of whoever you shared them with. So what does this do for the URL that was just shared? I believe it depends on who did the sharing, who is in their stream, and any existing link graph Google has for the shared URL. If it’s a brand new URL, that could lead to a crawl, and if the URL was of quality in the first place, that will lead to natural attraction of links, tweets, pluses, etc., just like any other site/URL would. Get the full story at Search Engine Land