I strongly recommend to go see Joe Kraus talk Slow Tech where he talks about the way we're creating a culture of distraction and some of the effects of this.
Don't worry. It's only 15 minutes long and you'll be back to browsing & email before you know it :-)
I've noticed myself that I seem less able to focus than I remember. This may be partly age I suppose, it may be ADHD (which I think I may be mildly affected by and am reading about), but I think it's also about how we consume information now.
I watched myself in a cafe last night fail to achieve any one goal be it to read a chapter of a book, read a page, write a complete document, etc...
My brain would flip from one task to another because it was so easy to do so. I'd be reading, a thought would come up, I'd switch to the browser, then get distracted by another tab, ..., finally remember the book.
It's for this reason that I no longer have an email notifier and have turned off Twitter notifications. In fact I routinely turn off notifications in iOS applications and make heavy use of the "do not disturb" feature on my phone.
The powerful thing Joe notes that where we would have once had space to think (e.g. in a queue, on the station platform, etc) we habitually reach for our phones now. Time that might have been spent in thought is now spent consuming other people's information.
I'm trying to take Joe's advice and slow down.