I've been looking for some sort of "tool" which would enable me to share notes, ideas, images and make my overall brainstorming process on specific projects a bit more intuitively shareable with certain people.

I had been using Day One, in general, to document thoughts and ideas and it has been working like a charm for me. Just me though. So, as I try to involve more people with my new ideas and projects, and since my "business partner" is not even based in the same country as I am, shareability and the option of -not only sharing, but also- editing notes and ideas by both parts seemed to be impossible to find (don't even mention Evernote, which seemed like the best solution, yet, the free version allowed me to do squat!). 

A few searches later I found myself accross Springpad: a fairly simple sharing platform. One could  describe it as a more content-affluent, more flexible and quite more elaborate version of Pinterest, but I wouldn't want to do that because Springpad allows you to do much more than just pin & share. (Don't get me wrong I love Pinterest but in a scrapbooking kinda way)

SP allows you to create private Notebooks which you can share with people you chose to invite. You can categorize what you post (though I do prefer to go with plain ol'notes for everything) and you can use tags for your notes (which makes it magically easier to find all those #Brainstorming notes). 

Both the iPad and iPhone apps look good and work even better (especially the iPad app), but the  browser-based version is surprisingly stable and very efficient.