For me, the most important things I do on my computer are my programming work, checking the web to see what's going on out there in the world, and managing my email. Over the last year or so I figured out a few techniques that make these things easier to handle. For programming, I've learned a lot more about how to get around in EMACS, and have switched as many projects as possible to Ruby on Rails. For the rest of it, well I haven't managed to get all GTD or anything, but things are at least a little less chaotic than before.
The key is to harness the FLOW. Things happen to you in life like you're standing in a river. Too often, we try to pin things down before trying to address them - this is like trying to hold water back with your hands. The way to manage something that's flowing is to flow along with it. We can't be completists these days - it's just impossible. Learn to accept that, and try to catch the good new stuff as it comes by.
A few technical changes over the last few years have helped make this easier: search has become powerful and ubiquitous, and almost everything has either a tag or a timestamp or both on it. Take advantage of these to take more control of what's coming at you.
This was originally one post, but I got carried away and it got rather large, so I'm breaking it into three. Hopefully people will find it as useful as it seems they're finding the Reading Sideways posting.
Mail. A very very long time ago - I think in 1993 or so - I actually read and handled every piece of email that came to me. Of course, I was only getting email from about ten people, and only two of them from outside Oberlin, so this wasn't difficult. Once I got out into the real world and the internet started growing, I rapidly started losing control of my inbox. The tools improved, but the volume and my life kept falling behind. I had folders for various topics and people - but I didn't know what to do with the many emails that seemed to apply to multiple folders. I had automatic scripts that fed messages into folders - but then I found myself having to check each folder every time I got my mail, in case I missed something.
The recent few iterations of OS X's mail.app have changed this. The program includes a very fast and easy search functionality - if I want to find something sent to me recently by Signs of Change, I just type '@signsofc' and click on the column header for date and - pow - there is everything that came from (or was sent to) an address at Signs of change, sorted by date. If someone wants to double-check an invoice that I sent, I type in the number and - pow - there it is. The best thing about this is that I don't need to organize everything by folders anymore - I can never predict how I might want to look for my information some time in the future, so I could never get a really useful folder structure. With search, the messages are organized at the time that I'm looking for them.
The other nice feature in mail that makes my life easier is Smart Mailboxes: these are like Smart Playlists in iTunes - you can set them up to include messages that fit certain criteria, such as sender, subject, or by date, and even relative date.
I spend 98% of my time in Mail.app in one Smart Mailbox, called 'Unread & Flagged'. It has two simple criteria: include any messages that haven't been read yet, and also include any messages that have been marked as flagged. This Smart Mailbox is home to my 'flow' - it has new stuff and important stuff, BUT NOTHING ELSE. Messages come in to me all day - some are spam, some are from mailing lists, some are automatic notifications from systems that I've built - and if they're important, I flag them. If they stop being important I un-flag them. If they're not that important, I don't read them until later. If I read a message and either reply quickly or don't want to bother with it, I don't flag it and it disappears on the next refresh.
Every so often, I go through my old flagged and unread messages and clear them out. I don't this often enough, so I do have quite a lot of old messages at the bottom of the list - but 315 (current count), most of which are at least important in some way, is a lot less than the thousands I used to have back in my old Lotus Notes client in 2000 or so. Clearing them out is easy too - just mark them as read or unflagged and they're GONE from immediate attention, but still available to searches. No more figuring out which folder to put it into or whether I should delete it or not.