Any serious webmaster knows that good incoming links are going to be the lifeblood of his website. One great way to get incoming links is to be active in the social media circuits. Here's a quick rundown on the ins and outs of incoming links from major social media sites.
You're going to read the phrase 'link juice' quite a lot here, so I thought it might be in order to have a quick rundown of what link juice is:
Basically it's the share of a page's authority with the search engines which gets passed on to the page that is linked to. This is affected by a lot of factors though. Negative impacts are:
Pages that have more than 100 outgoing links
Highly commercial pages that have more than one adsense campaigns associated with them
A large number of paid or sponsored links
A page with lower Google pagerank than your own
So as you can see from these points, links from a successful social media site could benefit your site greatly--if you could only get links that pass juice.
Before we start let's get one thing straight: most of the social media sites no-follow all links, which means that they don't pass link juice to your pages. But as we'll see, you can still benefitgreatly from having incoming links from social media venues.
Back before the social media sites started changing the status of links to no-follow, having a lot of social media profiles was compelling. As is the case with most great things online, the spammers ruined it for us and a lot of sites started implementing a no-follow clause for outgoing links. This process is continuing even as we speak; daily more sites become no-follow.
But as with everything in life, there are ways to get the links you need.
Take FaceBook for example. It's true that Facebook links don't pass juice. But if you play your cards right you can still get useful links. Using FaceBook markup language, or FBML, to customize your pages can result in links that pass SEO credit. Hubspot's recent article on the subject gives more detail on that. I'm not sure how much use this would be and how many links you could garner from a page, but it's worth a try if you absolutely must have some FaceBook linkjuice!
Twitter, for a while, did not implement no-follow so spammers were clamoring for Twitter links. As a result Twitter no-followed bio-links, but links in posts are still technically do-follow. However, some are saying that there is no link juice from TinyURL, which is the URL shortener used by Twitter. The theory of no linkjuice from Twitter has by no means been proven inconclusively yet, and in the bargain, lots of Twitter posts show up elsewhere on the web as they are indexed. So you could still end up getting juice for them. A good strategy to follow is to create an account with FriendFeed and feed your Twitter updates through that account because FriendFeed does not use no-follow. Heck, just post your links (naturally of course) to FriendFeed.
One more point on Twitter: if it turns out that TinyURL isn't passing link juice but that other URL shorteners are, you might think of using Twhirl which offers users the option of three different URL shorteners.
Another great social media site that does not use no-follow is Stumbleupon (this has been contested but for now we'll assume that SU is still passing juice). If you participate in the right way, which means reciprocating and not spamming, and if possible not submitting your own pages, you can get a significant amount of traffic from SU too. If you want to avoid being penalized by SU, don't make the huge mistake of submitting your main page: submit each individual blog post for best results (that is, get someone else to submit it!).
Mixx also passes linkjuice as of this writing. This is a comparatively new bookmarking site, but it is fast gaining ground on Digg, especially since Digg banned a huge number of power-users in 2008, forcing them elsewhere--they nearly all ended up on Mixx giving that new venue a huge boost. Incidentally, Digg itself also still passes linkjuice.
With an enviable Google PR of 9, Slashdot also passes valuable linkjuice, so don't overlook that one.
You will get more chance of getting pages indexed from your social media accounts if you use them regularly. Participation is key to successful social media link propagation.
Getting the Most LinkJuice from WordPress
Lastly: if you choose to use WordPress for your main business website (as SEO-Scoop does, and as I do over at Wellwrittenwords and as many other successful businesses do), you can use a do-follow plugin. The advantage to this is that it actually encourages readers to comment and to link back to you from their sites.