I've been into online notebooks for quite some time now, mostly because I find it very convenient to have quick and easy mobile access to the notes I create on my laptop. I've mainly been using Evernote, which I still find to be the best one out there (and I'm not the only one, apparently). There's only one nasty problem with it - try looking up these notes when there's no coverage or you just don't have mobile internet access right then and there. You can't - or at least I haven't figured out a way to do it.

Enter Springpad, which does give me offline access to my text notes - that's about all I use it for (I still use Evernote for the rest), but to be fair it does have some other nice features as well. It's definitely worth checking out!