Let's face it: everyone's attention span seems to be continuously shrinking.
Although I imagine that this is mostly a byproduct of the internet and its inherent information overload, I don't think it's strictly a digital phenomenon. You may notice that your attention span has shortened even when it comes to, for example, reading a newspaper or magazine article (how many of you skip an article that is longer than two pages?), and while performing tasks at work.
You may notice, however, that interestingly enough, it rarely happens while you are immersed in a good novel. Provided that external distractions can be turned off, most of us can still get lost for hours while reading.
So what does this mean? Does our attention span vary depending on information and activities? Does it correlate with the amount of external distractions we experience? Would focusing on a task be simpler if the web browser button weren't so immediately available and e-mails didn't rush in continuously?
This is certainly a big part of what causes the problem, and being aware of it helps tune in to our higher attention potentials. We can't, however, avoid being part of the digital age (nor would we want to), which is so beneficial and empowering from a number of other perspectives.
What we can do is raise our level of awareness of the limits of our attention span, and strive on the one hand to improve them, and on the other hand to learn to use that span of time in the most focused way possible. For example, if you know that your maximum attention span is 15 minutes, why not divide the task you need to perform into smaller bits that fit into that 15-minute block and schedule minor activities (phone calls you need to return, a small search you want to carry out on the internet, etc.) in between?
I find that writing down a plan (or list of activities) for those flickering moments when attention to the main task fades is an incredibly useful way to make the most of my attention waves. It also helps focus back on the primary task: once the list of minor activities is finished and ticked off, a phone call returned, Facebook checked and daily news read, you have nothing left but to go back and refocus.