I keep gmail on till the time I'm in office. When I'm at my desk, keep checking it every now and then, perhaps every 10 minutes! And even while I'm doing that I realize that my concentration's getting disrupted. Not just that I'm pretty sure it tires me, makes me anxious. Can't I do that twice or thrice in a day? In fact, most often when I check I do not see any fresh mails. And yet after knowing this for quite some time, I continue to do it every day. A high cost I pay trying to keep abreast with my emails.
For a better understanding of what I mean, refer Seth Godin's article 'The high cost of now'.