On Friday, I sent 13 emails and received about 40. 10 of those 13 were responses to others. Many of these were planning meetings or events where faster responses meant more got done today. This was not particularly unusual for a weekday. A couple of these were ones where we proceeded to have a conversation. I am a college student, but I am the leader of a couple groups on campus and heavily involved in a few more.
In my case, where about 1/4th of the emails I get need a response, I would say my current method of having a small pop-up come when I get an email works pretty well.
The once a day method works for people who don't need to respond, or response time is less important. But that's not true for everyone.
How frequently do you think you *should* check email? You can also say how frequently you do in comments.
Personally I'm sold on thinking you should check it around once a day, not necessarily without fail. That increases focus on both email and non-email, and minimises getting sucked into distractions. But some people I know disagree. Some believe in getting notifications whenever a new email comes in.
For anyone who'd like to check email less often and uses GMail, I recommend using http://inboxpause.com/ and this full screen compose link: https://mail.google.com/mail/u/0/?ui=2&view=cm&fs=1&tf=1&shva=1
Edited to add: I'd recommend everyone at least try checking only once a day, at least for a few days, to see if you find it more productive and/or relaxing. That'd be a big enough win to make experimenting worthwhile.