From what I can see, there is currently only one realistic alternative to Google for getting any significant amount of free traffic, and of course that's Bing (which also powers Yahoo). It appears to me that Bing still rewards quality and value with high rankings.
Yes, Bing (and Bing-powered search sites) combined only have about 25-30% of the total search share, but they are no longer losing ground to Google, and may have even started an uptrend. In any case, 25-30% is certainly worthwhile in many cases. So I don't think Bing should be ignored, assumimg that it doesn't follow Google's path to worse and worse search results.
Unfortunately some webmasters have harmed their Bing/Yahoo rankings by trying to please Google. Some have made drastic changes to their sites, and some have even tried to get backlinks removed. I haven't done any of this myself, and the Bing rankings for all of my sites have actually been improving. On one Penguin-hit site, the Bing/Yahoo traffic is now almost as much as the Google traffic, and on my other Penguin-hit site, it's about two-thirds as much. It's still a lot less for my non-penalized sites, but who knows when Google might penalize them too.
P.S. My sites are informational, and the situation might be different for commercial sites. Maybe someone that knows more about this could comment about any differences.