In the case of WPHub.com I’ve never needed to purchase any links because there is so much high quality content on the site. It’s in an industry where it’s easy to get people to work with you. Unfortunately in other industries I work in that isn’t the case and some of those sites got hit with the Panda update. The best advice I can give is this:
1) Only post content on your site that is AMAZING. All your content should meet the following standard: “The person reading the content will find it to be useful and take something away from it they didn’t know going in. The content is so good they feel compelled to like, tweet, or link to it”.
2)Never ever buy a link and stay away from link directories.
3) If you’ve been hit by Panda go check out ahrefs.com or SEOMoz.org and start emailing all the trashy sites that link to you and work on getting the bad links removed. Matt Cutts himself came out and said that no penalty lasts forever and with each update these algorithm type penalties can reset. I’ve already personally had success in getting a few sites ranking again and there are a couple great case studies out there you can find with a simple Google search that can guide you on how to fix things.
4) If you got hit by Panda it’s because you cheated and / or are lazy. It’s that simple. Stop trying to cut corners and work on building a quality site. If you do that you won’t need to worry about Google updates, but look forward to them. Google sits in a room everyday and tries to figure out how to get quality sites to rank higher. Focus on building a quality site with a great user experience and you’ll be happy in the end.