Parece que saíu uma versão do Google Desktop para Mac. Parece que aquilo indexa e procura o que quiserem não só nos folders, mail e etc, como o Spotlight, mas também na web.
Parece permitir ver versões de ficheiros antigos ou mesmo de ficheiros que foram apagados.
Tendo em conta que isto deve levar uma parte do espaço em disco, não estou muito bem a ver porque hei-de instalá-lo, quando já uso o Quicksilver, que para além de todas as funções de procura mencionadas ainda me permite automatizar processos, criar ficheiros e enviar itens para applicações

I tried several GTD applications to help me to organize what I have to do. The last one was Actiontastic and although I was very impressed to the easy way of working with it, I really had to return to Ready-Set-Do!
And the main reason was that this group of scripts warn me to do my reviews, something that I did not found in the other apps that I tried. At the time I defined on iCal there is a box that jumps on my screen and I have to process my Inbox itens. One other reason was that Ready-Set-Do! asks questions during the process, which helps me to put things in the right place.
And you have the other possibilities too: send to printer or to your PDA.

In the site, you can download a movie (which explains all the process) and a Free Trial. Browse the site to see everything that Ready-Set-Do! can do.

I think Journler is one of the best apps for MacOS X. You can organize everything in there: you can link files on your computer or import them to Journler.
If I am writing about a book that I have classified in my Bookpedia, I simply drag the title from Bookpedia to Journler and it creates a link that open Bookpedia in that book.
If you want to take some audio notes or even record a movie you can do it directly in Journler.
You can make posts on your blog from Journler or send your writings to your iPod.
And, of course, Journler has integration with iPhoto, Mail.app, Adress Book, iTunes, iMovie and so on…

The personal license is donation based and you can check all features here.