Sadly, I am not a naturally productive person (organized: yes, productive: no) so I rely on numerous digital crutches to help me.
The main two applications I use to track my growing list of to-dos are iCal (can't wait 'til v3) and Schoolhouse (a homework tracker, and so much more). I generally use iCal to schedule my MANY social engagements (note sarcasm) and misc. to do items while Schoolhouse is for my homework (what else?).
In order to maintain some degree of mental togetherness I also use Sidenote to keep all my floating brain snippets caged up in one place. (For those of you unfamiliar with Sidenote, it is like Stickies except everything is kept in a tidy drawer that can be hidden from view, ideal for people (like me) who are
lacking in miserly when it comes to desktop real estate).
iGTD has been getting a fair amount of press (in the blogosphere) lately, so I tried it. I was delighted by its frequent updates (I live for updates) but it was just too data heavy and I didn't really get anything from it that iCal couldn't give me (plus iCal looks better). Sadly, after several weeks or trial I had to delete it.
Many Mac users swear by Quicksilver but when I tried it (after finally giving in to the raving reviews) it just didn't work for me. I have been with Macs for a long time and I'm just too used to Finder for launchers to do me much good. (Yes, I know Quicksilver is more than a launcher but the only other feature I ever really found useful was the built-in iTunes controls). Bottom line is I'm just too used to my mouse/trackpad to start filtering my workflow through key sequences.
One tool that I have NEVER seen any use for is Event Maker (and other iCal event creators). Although I will be one of the first to admit that iCal's event creation process can be a bit frustrating it just isn't worth it to open up a whole new application to make it easier. By the time I have found and opened the app I will have already sorted out my problem with iCal.
Straying away from the digital realm for a moment, the hPDA is an interesting organizational/productivity tool that I used for some time before it fizzled out. I was mainly using it as a paper Sidenote for when I was away from the computer, but a combination of the inability to synch (honestly, paper manufactures need to get on that) and my increasing attachment to my computer rendered it more or less useless. (However, I do still use it when I AM away from the computer or when pulling out the laptop would be overkill).
Also, for some strange reason, spending hours in Excel charting my time use just didn't make me more productive....
What Keeps Me Unproductive
I consider Adium to be the best chat client ever (and therefore the best at distracting me from my work). I am almost always online and I am usually being distracted/kept up too late by messages.
Vienna is another of my productivity-sapping loves. For those of you that have not aware, Vienna is a news reader (like News Net Wire Lite, except it takes less then ten seconds to say and is about 100x better in every other way too). I now call upon all you users of NNWL to switch to Vienna and see how you like it. It is basically Net News Wire (the non-free version) except with a better interface and (even) more features (plus a cooler name).
Safari and the internet are the biggest culprits when it comes to reducing my productivity (I'm sure I'm not alone there) but I figure the time I would otherwise be spending trundling back and forth to the library probably balances it out.
Finally, although I love you so, Growl, you are the one who pulls all these elements together into one big unproductive web. Without your little boxes I would never know when Vienna had new articles or when I had gotten email or when someone was IMing me. (On the other hand, knowing my personality, I would check every ten seconds for new badges on my (hidden) dock.)