When I'm working with my main client, I find myself using the email archive feature of DEVONthink Pro Office many times daily. This is owing to the fact that the search engine within DEVONthink Pro Office is second to none and I find myself having to do a LOT of email searching daily.
I also need to open a lot of these emails in order to request more information, open attachments or perform other actions. To do this, it's a lot easier to open the emails within Mail.app (or whichever is your mail application of choice) than within the DEVONthink Pro Office application itself. There is a menu shortcut to do this (right click, Open With, Mail (default) however when you have to do this as many times a day as I do, this can get quite onerous (yes, I know, first world problem....but then I'm a first world person!)
A quick bit of digging showed a keyboard shortcut for this (⬆⌘O) which saves some time. However, as my regular readers will know, where there is a keyboard shortcut, there is a BetterTouchTool gesture that will perform the action ever faster!
So that's what I did. I configured BetterTouchTool to open any given file within Mail.app whenever I double tap on my touchpad with four fingers.
Such a simple hack, but one that I use at least ten times a day, so cumulatively saves me a lot of time.
While we're on the subject of BetterTouchTool, I'd like to raise the point that it's now a paid for application with a 'pay-what-you-want' subscription model. This has been met with some...curious..comments on the developer's site, which I find baffling. Thankfully, most people realise how much time and effort goes into an application like this and how much time it saves.