I have my doubts about Google's new plan  to better target advertising to meet our transient interests. As yet another manifestation of the idea of only showing us the ads we want to see, when we want to see them, it will inevitably stumble over the reality that we often don't use the Internet in ways that fit advertisers' assumptions. Machines get shared, people use multiple browsers, and, increasingly, web users are savvy about being able to block ads, regardless of how targeted they may claim to be.
We're in an arms race with advertisers (and spammers, their less- reputable cousins): As fast as we improve ad-blocking technology, they improve their ability to get past it. This will only get worse as the Web becomes something we carry with us as a constant presence. But what happens when you combine increasingly immersive digital tools and aggressive competition between advertisers and filters? Unintended, and potentially quite unsettling, consequences.
Technologists and futurists call the mashup of digital info and physical space “blended reality .” Apps in development for the iPhone  and Google’s Android platform  are early indicators that a seamless blending of atoms and bits may soon be available to us. And just beyond that, personal heads-up displays, digital glasses, and other forms of wearable immersive systems, all of which exist in prototype may give us a view of reality seamlessly blending the Internet and the physical world.
Along with the Internet-blended reality, of course, likely comes advertising (and spam and viruses). These can be blocked, but the most effective steps we could take to put a lid on digital junk would ultimately undermine the freedom and innovative potential of the Internet. The more top-down control there is in the digital world, the less spam and malware we'll see -- but we'll also lose the opportunity to do disruptive, creative things. Consider Apple's iPhone App Store: Apple's vetting and remote-disable process  may minimize the number of harmful applications, but it also eliminates programs that do things outside of what the iPhone designers intended.
Blended-reality technology could play in a limited, walled-garden world, but history suggests that it won't really take off until it offers broad freedom of use. This means, unfortunately, that ads, spam, and malware are probably inevitable in a blended-reality world. We're likely to deal with these problems the same way we do now: Good system design to resist malware, and filters to limit the volume of unwanted ads. All useful and necessary, but there's a twist: Filtering systems for blended-reality technologies may allow us to construct our own visions of reality.
Why? A blended-reality interface  won't be just a dumb display we carry with us or wear on our faces. In order for it to be able to properly display digital images mixed in with real-world objects, it would need both a camera and sufficient smarts to be able to recognize what it's looking at. Most discussions of blended reality suggest that we'd want the technology to observe the world around us in order to "notice" things we'd find interesting. Connected to the Net and various data sources, such a system would be able to tell us quite a bit about what we're looking at.
With such technology, it's a small step from blocking digital ads to blocking physical ones, too. The camera-enabled blended-reality device could easily include a feature that not only blocks the digital ads we don't want to see, but also billboards, fliers, and maybe even branded clothing.
Of course, all of those blurred-out spaces can get distracting, so we'd want to replace them with alternative images -- perhaps photos pulled from our own online galleries. The substitution doesn't have to be perfect; it just has to be enough to not interrupt our attention. In fact, we'd want it to be slightly imperfect, so that we don't mistakenly try to read (or point other people to) something we're blocking.
This may sound appealing, but it has a dark underside. The moment that we can easily display location-aware images on a blended-reality system, people will try to block any images they don't like. Forget ads: Some people will block even slightly suggestive images, or signs proclaiming religious beliefs that they oppose, or newspapers and magazines with arguments they don't like--anything that would upset their custom-built reality. Or maybe anyone. Consider the "Prop 8 Maps " site, mashing up Google Maps and public records of people who donated to support or oppose the 2008 California proposition on gay marriage. Suddenly, you could easily see who around you agreed or disagreed enough with the proposal to put up money.
That's not too hard to imagine. Face recognition technology is progressing quickly, and often relies on the same heuristics that enable the recognition of physical objects. This means that, technologically speaking, it's not too far of a leap from blocking advertisers to blocking out the people who annoy us. With one click, we construct our own realities, ones that don't include the ideas -- and people -- we dislike.
The future is made up of unintended consequences, and this could be a big one. Blended-reality technology is the ultimate expression of the mobile Internet wave. But it looks like the flip side of "show me everything I want to know about the world" is "don't show me anything I don't want to know."
Related link: MIT's Sixth Sense Machine Makes Reality Better 
Related link: Why Your Next-Gen Smartphone Will Do Proper Augmented Reality 
Jamais Cascio covers the intersection of emerging technologies and cultural transformation, focusing on the importance of long-term, systemic thinking. Cascio is an affiliate at the Institute for the Future  and senior fellow at the Institute for Ethics and Emerging Technologies . He co-founded WorldChanging.com, and also blogs at OpenTheFuture.com .