SEO tactics follow a very predictable life cycle. When first they are identified they just work. But their use is limited to small groups who may or may not have discovered them independently. It’s execution may or may not be automated at this point, but it hardly matters, as it’s still only a very slight signal lost in all the noise.
The next phase starts when they get shared. This phase can take ages, an idea or tactic can slowly spread through parts of the greater SEO community without ever really making an impact. At least until it finally reaches critical mass and becomes a standard practice. Once an SEO tactic becomes a standard practice it’s heading towards it’s terminal phase. In the past Google would just quietly start to develop ways to ignore it, or adjust for it’s influence. These days they might associate a negative penalty with it.
In short as a general rule, if an SEO tactic works, is popular and some have sought to make it scaleable, it probably has a short useful life.
Where go you think this blog post from Matt Cutts would place Guest Blogging?