Some think that sentience could emerge from any sufficiently complicated system. By the way, you're reading this on a massively-crosslinked network built from millions of routers, allowing any of a billion individual units to access, modify and reply to the others. Interested?
Computer programs are already exhibiting many of the characteristics of organic lifeforms, up to and including evolution - hilarious, since they're the only things that really are "Intelligently Designed" - and there's no reason to believe that life or awareness are exclusively organic attributes. You could say we've only ever seen chemical-based constructs which are alive, but in the past the same argument could have been applied to things moving under their own power, flight or the ability to count - and it turns out we've built machines that are sort of far better at all those things than the fleshy equivalents. If there is a magic "life-chemical" mixed in with all the blood and guts, we haven't found it.
Others would object that only beings with souls can ever be truly alive, but such people rarely have anything useful (or even sensible) to say on the subjects of evolution or technology and so can be safely ignored.
The question is now what form this life would take. While the movies teach us that evil cybernetic intelligences are created in military research labs, with the occasional time-traveling component mixed in, the most likely environment is wherever has the greatest connectivity, diversity and sheer quantity of data flow. That's right, the internet.
One route is the evolution of electronic intelligences in situations like the internet-arms race between spammers and shielders. It might sound silly, the idea that new life could be created in an attempt to offer you a great deal on C1@Lis!!, but have you tried registering for a forum recently? Even gaining access to the lowest level of interaction online now requires elementary Turing tests to tell the humans from the robots.
Another option is the idea of the net itself becoming sentient, a vast self-modifying array of connections and information storage with limited connections to the outside world (kind of like that glob of grey goo you carry around in your skull). If that happens then Gibson help us all - remember that the net is made of about 90% spam, 9% porn, and quite a lot of whining blogs. If that mixture ever becomes self-aware we're not quite sure what it'll do, but the odds are against it being anything good.
Posted by Luke McKinney.