SEO is ever changing and evolving.  What might be really important right now, may be much less useful in a few months.  It's important to keep on top of things.  One area that, in my opinion will never go away, and only grow stronger, is Twitter.  The use of Twitter is a vital free tool for improving search engine rankings, as well as direct traffic to your site.  Since Google, Yahoo and Bing are now indexing "Tweets" in search engine results, the use of Twitter is one of the best free marketing tools out there.  There are also hundreds of thousands of applications out there that make using Twitter even more convenient and fun.

Another important tool that has grown in importance, and will not go away is the necessity of linkbacks from other sites.  Using tools such as Digg.com, Blogs, and article submission sites are a great way to help add linkbacks to your site.  Search engines rely heavily on inbound links to a site when considering a ranking- so don't underestimate the importance of inbound links.

SEO has always been about 2 things. Content – correctly displayed on your site, and inbound links pointing to that content.

At one time in the early part of this decade, it really did not matter where these inbound links came from. You could run exchange link programs, grab slots on numerous paid or free directories, and build an umbrella network of your own sites on one shared server to boost link credibility.

From the middle of last year that all started to change dramatically. Now in order to maximise the placement of your site in major search engine results pages you need to develop a link building strategy that in the main produces highly focused and authoritative one way inbound links to your site.

3 or 3 years ago we were all way too focused on PR value of the links we acquired, well guess what, it was a Red Herring!   PR matters so little now, Google are having meeting to discuss removing it from the Google Toolbar.

^Today's SEO needs to have the understanding how to undertake original and innovative schemes to facilitate inbound linking to his or her clients web sites. There are also more bases to cover. When Google Search was king, you didn't bother with much else, maybe Yahoo! being the exception. Now Google Youtube get more hits than Google Search. If you haven't got video content, you're missing out on your biggest window to visitors.

Facebook has also changed the SEO element so much so that the job title has now been compartmentalised in to SEO and Social Media Marketing (SMM). In the middle of last year Twitter introduced a follower hierarchy based search tool. Get a million followers and you can now be number one when you tweet daily on any subject you like. 

Quality content and inbound links remain important to SEO. It's important to keep an eye on changing trends as well, such as Google's recent announcement of using page load time as a ranking factor (albeit a lightly weighted factor).

One thing to keep an eye on is the slow but hopefully steady movement toward a "semantic web". While we're still a long way away, efforts such as Facebook's try at building a "semantic search engine" are something to keep an eye on. Andy mentions above the power of exploiting social networks. As Facebook, Twitter, Flickr, and other social media outlets continue their growth, this can become a force to reckon with. My concern is that the masses of "likes" will be along the lines of "keyword stuffing" to rank high in traditional search engines.

My plan is to follow Andy's recommendation–focus on quality content and finding the right social network demographic to attract traffic–let the rankings follow.