When I started in the SEO field (circa 2003), the job responsibilities weren't easy, but the list was relatively small. Over the next 5 years, those responsibilities increased, but it was primarily in tactical and knowledge sorts of ways. A 2003 vs. 2008 rundown might look something like:

(Notes on image above: There's some over-simplification in this list, and some items cross the artificial 2003 barrier a bit)

The last 2.5 years, however, have made for some fairly substantive changes. We're facing large-scale, industry-shifting trends that have upset the classic model for search engine optimization, including:

• Google's Vince update and others like it where search engines are biasing toward brands over smaller, lesser-known sites.
• Panda and the focus on user behavior, trust and authority of sites based on their look/feel/content style/etc. has changed what it means to do SEO, just as the Florida update did at the end of 2003.
• The shift in web user behavior toward social media - more than 20% of our time spent online is spent on social.
• Fragmentation of the social media market: LinkedIn just passed MySpace to become the #2 social network in the US, and Twitter, Facebook, Tumblr, Reddit, StumbleUpon (and soon, Google+, IMO) all have 10million+ active users. FourSquare also just passed that mark.
• The powerful increase in content creation as a marketing tool for businesses. 57% of companies in Hubspot's recent survey run an active blog!
• An overwhelming increase in mobile and, thus, local search/web usage leads to portals like Google Maps, Bing Maps, Yelp, Citysearch, UrbanSpoon, FourSquare, etc. offering massive potential value to local businesses and service providers.
• The recession in 2008 caused a massive change in how businesses think about employment - human resources are nearly the last thing companies will add to their costs, and while that's generating amazing profits, it's having a rough impact on employment. As a part of this trend, SEOs have been asked to shoulder many new and heavy burdens.

Thus, we're faced with a picture where the responsibilities of SEOs looks more like this:

(Note: Some of these are due to changes in SEO itself, and others due to the additional expectations placed on those performing SEO)

If you're in the SEO field, this shift is both a positive and a negative. If you can keep up with the workload, manage all the metrics, reporting, data and platforms AND perform effectively in all of these spheres, you're likely able to charge outsized fees (or earn a much higher salary). If you remain tactical and niche, you're either going to be undervalued or you'll need to find ways to make that specialization and the ROI you can earn visible to your clients/managers.

The job of an "SEO" is so much more than what we think of and talk about as the basics of classic "Search Engine Optimization" that it almost feels as though we deserve a new title... and probably a raise :-)