Let's say that we have just finished setting up and outsourcing a campaign with a third party optimization company. They did their thing, emailed you what they did and claimed your website is now ranking higher for a set of keywords that are highly relevant and sufficiently enough searched for.
You have the data, you've double checked it and everything seems fine. Euphoria sets in and now you have that unreal feeling for a couple of days. Traffic has increased, revenue is better than ever and your website is simply doing great.
Then one day after a couple of weeks, you routinely login into your analytics account and find out that your traffic has dropped by ONLY 90%, as well as revenue. This is also an unreal feeling, but this time it's the unpleasant one. You know your project is probably crippled for life unless you radically change something.
Google is now sending you a fraction of traffic that it used to. And it's all because you've tried to game the system just like everyone else who's complaining about the big bad new algorithm update.
Well, "we" had it coming. No point of bashing our heads against the wall now. All of us who got hit real bad need to realize that if we expect Google to make our lives easier, we need to make Google even more richer and powerful by paying for every single visitor that it sends to us.
Search engine optimization, or better yet, Google optimization just got real. It's time for all of us small players to grow up and understand where we belong.
I would say that SEO is as reliable as it can be and none of us should concentrate on that alone. As a bonus traffic generation method, sure, but as the only one? Not a chance!