The difference with my workflow is that I always have a multi-tab outliner open (the OPs aforementioned Ecco Pro). A thought crosses my mind on any one of the many projects that I'm working on, I flip to that tab and write it in. Then, when I'm working dedicated on the project, I go and organize. The one-doc/one-outline approach of Word/Pages doesn't cut it for me, and I've always have found the Word/Pages outline features clunky.
So, Evernote is SO close to meeting my workflow model, and in fact could better it, being able to really quickly open up the right Note (equivalent to my tabs, without the tab limitation) as well as all the other great organization features that Evernote brings to the table.
I know us outliner junkies are not that common. I would dearly love to move away from Ecco, a program that was Windows only, follows none of the current GUI standards, and was abandoned in 1996. (BTW, I'm on a Mac, and run Windows under Parallels just so I can still run Ecco...) But I have never found anything better for outlining. Evernote could be.