Evernote is an service/application you can use to store notes, images and all kind of information (like audio, handwritten or video notes) for retrieving later. It supports search and tagging and most importantly: you can sync everything between computers - further more, Evernote supports mobile devices too like iPhone, Windows Mobile, BlackBerry or Android and there's a web interface too and a clipping bookmarklet to pull anything into your netbook. But unfortunately there's no official Evernote application for Linux.
NixNote (previously called Nevernote) is an open source clone of Evernote that works on Linux. While Evernote now runs on Linux through Wine, the application is quite slow so you may want to try NixNote.
NixNote supports most of the Evernote features so you can easily drag and drop images or PDF files, tag or preview notes. Unfortunately, there are some features which are not supported by NixNote: you can't write ink notes or record webcam notes, there is no screen clipper (but you can use Shutter instead!), emailing only sends a plain text note and also the sharing feature is missing.
On the other hand, there are also quite a few features that NixNote provides which are not available in Evernote, such as: changing the background or title of any note, highlight text, encrypt the database at the database level to improve security, theme support, display PDF files inline or as a file icon you can click later, rotate images, close netbooks and many more.
(NixNote displays PDFs inline)
Further more, NixNote supports customizing shortcuts, but not through the user interface. To see how you can configure the keyboard shortcuts (there are already some default keyboard shortcuts so you only need to do this if you want to change them), download the Nevernote source, extract it and in nevernote/usr/share/nevernote read the "shortcuts_howto.txt" file. There are also some example shortcuts in the same folder ("shortcuts_sample.txt").
NixNote would be enough and I wouldn't miss any Evernote feature if only it would look better - there's always the web interface / bookmarklet for most of the other stuff I need. Because NixNote is written in Java / Qt, it doesn't integrate well with the Gnome desktop and looks... let's call it "weird" (I'm being nice here). But don't get me wrong, NixNote is actually great - or at least better then using the Evernote client under Wine, as long as you only want to take text notes and insert some files and get them synchronized with Evernote. If you want more, you're out of luck for now.
On the other hand, Evernote for Windows doesn't look too good when used on Linux either:
Hopefully NixNote will integrate better in the future or who knows, we might even get Evernote for Linux.
Note: to get NixNote (previously Nevernote) to synchronize your notes with Evernote you'll have to go to Edit > Preferences and under "Connection", enter your Evernote userid and password and select a sync interval (I also suggest selecting "Automatic Connect" and "Synchronize on Shutdown").
Download Nevernote (includes .deb and .rpm files)
Update: Nevernote (NixNote) now has an Ubuntu PPA!
Have you tried NixNote / Nevernote or Evernote under Wine? Which do you like best?