When I first got my iPod touch and upgraded it, one of the applications I just couldn't work out the purpose of was notes. You can create a set of notes on your iPod/iPhone but these don't get sync'd back to your desktop. The only way to get notes off the iPod is by emailing it to yourself. There is no way to create a note from an email, or from a web page by any means of clipping or pasting which means you needed to type it in, on the iPod. So, I used it for writing temporary notes which I could email to myself - maybe notes at talks, journal style entries when on holiday, that kind of thing.
Then mac mail gained notes functionality, and for a brief moment I thought that would solve the issue. But, rather annoyingly, the two notes applications didn't synchronise.
Then a few weeks ago, Richard, pointed me towards the Appigo Notes application - he'd bought the Todo application from Appigo and was pleased with it so I thought I'd take a look. This is an offline notebook (meaning that even with no wifi connection you can make notes/refer to existing notes) which synchronises with toodledo - a free online service for notes and tasks - and has a search facility. The application costs £2.99 and so far has been worth its money.
So, all of this means that if you're at a computer with an internet connection, you can type, or paste, information into the toodledo notebook and know that next time you sync Appigo notes that information will appear on the iPod, which is a lot easier than having to retype it all on the iPod.
Having bought this application, and being happy with it, I followed Richard's lead and bought Todo as well. These are still my only 2 paid-for iPod applications.