I this your question has as much to do with the expectations of the sender as it does anything... if they would expect a quick response, or have a perception that it is a small task requiring an immediate response then it might pay to communicate with the hour, with the answer or setting an expectation of when they might expect an answer.
Short and sweet, or with specific actions on their part to get additional answers you need.
If it's a longer term project, you could acknowledge receipt later.
I never thought about it before, but you could actually sort or flag emails by when it's wise to respond.
And here's some other things I do a few things to help manage emails --
Timeshift. I use boomerang for gmail to pre-write emails and then send them later... this could be work or personal (eg. birthday related)
I specifically use a blackberry over an Android or iPhone so I can type easier on the go, so I write emails on the go during otherwise downtime, like travelling from A to B.
Use #2 I write emails when I'm going for a timeout. So on my break sometimes I write emails OR I just take time away from the desk and stretch my feet while writing emails (I can type as fast on my blackberry as my keyboard -- fast on both).
I use autotext (on the blackberry) and a text expander (phraseexpress) to speed up the quality and time it takes to reply.
I write batch emails, in one 5-10min period I can reply to many (even if I don't send them all at once).
You can use followupthen.com to follow up unanswered emails for you.
You can use Toutapp for gmail to apply template responses.
For high prority people you can set up a watch list and auto-reply with an out-of-office to set expectations of reply times.
As a final aside, I keep cc/bcc to a minimum as I hate being copied on needless communications. And don't forget to pick up the phone if it can cut out a needless game of email ping-pong. That said I much prefer email as I can manage this and the time and method of my response much better.
I hope that helps a little.