When it comes to notebook applications, Microsoft's OneNote is arguably the most powerful product out there. Unfortunately, as I commented in a previous blog entry ("Is OneNote a Cul de Sac"), OneNote - in its current form - is very much a single user, single machine application. Getting data into OneNote is easy, but accessing it remotely over the cloud is not possible.
Perhaps the most popular alternative is Evernote. This provides a cloud-based service that is free when a limited amount of data per month is created (a limit I am nowhere near reaching). Evernote can be accessed through the website, but also provides clients for Windows, Mac and the iPhone. This makes it a very compelling product to use, even if it's not quite a feature-rich as OneNote. If using Windows, it's definitely worth using the 3.5 beta release as the interface is much better (IMHO) than previous releases and is more similar to the Mac version.
One of the things I like about OneNote is the Notebook/Section/Page metaphor. It's possible to have multiple Notebooks (e.g., Work, Personal etc.) and each notebook can have section tabs. Within each section, multiple pages can be created. In comparison, Evernote has the concept of notebooks and pages. In order to work around this, I adopted a naming convention for my notebooks that describes what each notebook is for:
Personal: Home Projects
Work: AIX Notes
Work: Business Planning
This effectively works around the lack of sections. (I actually realised after adopting this approach that when using OneNote, I only had a couple of notebooks for Personal and Work anyway and used sections to separate my data)
As for when to use a new notebook, I've adopted the approach that if I was to use a new physical notebook in real life (e.g., I'm attending a course), then I'll create a new notebook for it. This is what I did last week when on a Citrix XenApp course. All my notes were instantly available via the cloud to all my clients. I'm also using new notebooks for different projects.
Evernote isn't perfect. I'd still like the ability to click anywhere and enter text (like OneNote), and wish it handled proper text headings instead of just setting font sizes. But these are pretty minor. A native Linux client would also be nice, but the web interface works well enough for occasional use. One killer feature for me would be rudimentary drawing tools so I could illustrate notes with diagrams. In fact, I'd become a premium user for this feature.
Evernote is definitely worth a look if you're looking for a way to store all your notes together in one place, but access them from anywhere. A cloud win.