UPDATE: (In response to comment)
Attention span is a popular science construct. Related cognitive constructs include time-on-task and working memory capacity. The latter topic is often studied in a field called cognitive neuroscience. However, the former construct, time-on-task, is a difficult measure to study attention with because one may have to take into account motivation. Time-on-task or TOT is often used as a measure for motivation. In contrast, working memory requires the online updating of information and is associated with an individual capacity limit. Thus there is talk of "working memory span", the number of items a person is able to hold and maintain in memory for briefer intervals of time.
In popular science working memory has become associated with multitasking, and there are quite a few studies that explore the relevance of working memory for "dual-tasks" or more complex tasks, which require shifts of attention.
Memory has been one of the most studied aspects to understand our brains flexibility and malleability to change, neuroplasticity. Recent studies have demonstrated that it is possible to increase working memory capacity in certain domains, for example, in visuospatial tasks. This cognitive change has been found to change structures in the brain. Hence, plasticity is relevant for successful adaption to the environment - where the information and technologies are.
A cognitively demanding environment requires that humans adapt. To a certain degree, we successfully adapt, but the scientific literature has proposed laws suggesting that there can be too much of adaptation or sometimes not enough (see Figure 2 in Pascual-Leone et al., 2011), with consequences for whether we cope adequately with an increase of information. The goal is to reach optimal plasticity and thus optimal information coping. When it comes to selecting an appropriate information load, moderation appears to be key and gradual increases facilitate adaptive mechanisms (see Olesen, Westerberg, & Klingberg, 2004).
In conclusion, an increased use of technology can have both positive or negative effects on our ability to sustain attention as indicated by a stable maintenance required for working memory capacity. The way we approach technology decides the outcome.
Olesen P., Westerberg H., & Klingberg, T. (2004). Increased prefrontal and parietal brain activity after training of working memory. Nature Neuroscience, 7(1), 75-79. http://www.nature.com/neuro/journal/v7/n1/full/nn1165.html
Pascual-Leone, A. et al. (2011). Characterizing brain cortical plasticity and network dynamics across the age-span in health and disease with TMS-EEG and TMS-fMRI, Brain Topography, 24(3-4), 302-315. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3374641/