The e-mail is quite legitimate though sometimes I get e-mail that has no value at all. As part of workplace habits it helps to always think about who one is sending e-mail to; what are you expecting each of those people to do as a result of receiving it? That helps avoid group-reply lists that grow and grow and where the discussion has moved on so it is no longer relevant to the people at the start.
All sorts of distractions are the enemy of productivity because they don't just take the time it takes to deal with the distraction but the time it takes to get back into the groove with your primary task. Phone, instant message, e-mail and people coming up to you are all culprits. Working from home I tend to get less of the phone and people coming up to you and more instant message and e-mail.
My response is to avoid dealing with e-mails as they arrive but rather deal with them first thing in the morning and between other, larger tasks.
I too have an obsession with GTD apps. crazy. I've lost more time trying out new stuff than actually getting stuff done. Toodledo has been my final resting place but I still wander about. Trying Zimbra desktop right now.