Link velocity certainly is one of the signals that Google uses to trust and ultimately rank a site. But more important than velocity is how those links are discovered, which I believe also factors into trust. For example, if you sent a ping out to each of the 3,000 backlinks you built it would appear suspicious and devalue those links temporarily. I feel the same about RSS feeds or blasting entire tiers with one specific type of links (profiles, wikis, etc.). Ideally you want the links to be discovered naturally, which in today's world is a link pointing to your new link from the same domain it resides on. The fewer the footprints the better.
Assuming your backlinks are found naturally, the time it takes for Google to discover them will surely be spread out and reduce any impacts regarding velocity. For velocity to be a factor, there must be a baseline for analysis. New domains do not have comparable trends which can be algorithmically analyzed, which is why many suspect that a sandbox period exists. The sandbox does not exist as I've ranked sites in less than a month. What does exist are common mistakes that people make in building links that gets them into trouble and is counterproductive to achieving their goals.
Originally when the unnatural link warning issue was discussed it was believed that it was an algorithmic generated notice. Matt Cutts followed up after his initial interview and noted that 99% of the warnings that appear in WMT result from manual actions. Read
this page for more information and the follow up that Matt Cutts made:
The warnings in WMT are pretty much all related to manual actions taken against a site. Will they expire, and how long will it take? That is the million dollar question. I assume it depends on the severity of the case. Many believe that aggressive link building penalties will expire within six months. My experience indicates it's around 90 days, but once again no two penalties are alike as the severity of each case can vary. And I assume Google will base the severity and length of the penalty on a case by case basis.
I have recovered sites that received the unnatural link warnings by building more links using raw URLs, Domain.com and domain.com as the anchors. In fact, the unnatural link warnings disappeared in WMT within a day or two. Some sites that I have performed this same technique on have not recovered in the same fashion, but none carry the unnatural link warning they received. The reason why those sites did not recover is likely due to the fact that they are still over-optimized beyond my desire to re-backlink all pages with normal anchors or that an expiration on the penalty was manually specified by Google regardless of what actions I took to clean up the damage.
I recently 404'ed nearly every page on a site that I backlinked, except for the homepage, and have seen no results from that action. In fact, I have experienced a loss in traffic as my ranks dropped in Bing/Yahoo. Therefore, this is not an action I would recommend others use. Thankfully I have many frontline websites which I can test. If the sites burn, the income lost is negligible.
Some may see some sorts of rank fluctuations over the next couple of weeks as Panda fully rolls out in Japan and Korea. This will likely devalue some of their backlinks and impact those sites which are linked from such domains. As Panda spreads throughout the world, similar fluctuations should be expected. And on this note, Google does devote a fair amount of computing power to these rollouts, which is why they are not rolling it out to the entire world. This may be one of the reasons why people are not seeing quick results from their link building efforts. But then again, Google may be taking a different approach and treating every backlink it finds as suspicious until such links pass a more thorough analysis to determine if they are organic.
