The iPhone and iPod touch make for a convenient quick-look reference tool when you're using recipes you don't have a hard copy of. With the arrival of Dropbox for iPhone, kitchen life just got a whole lot more convenient.
You could, of course, always get at recipes searched out on web sites or emailed to you from your iPhone or iPod touch, but that requires a few clicks, and ignores the recipes you may already have stashed on your desktop or laptop computer. If you install Dropbox on your main computer and include your recipes in your synced files—whether by dropping a copy in your "My Dropbox" folder or using a symbolic link to sync any folder—you'll have a copy of all those recipes in your Dropbox app, and it's fairly easy to drop more in.
More convenient than just access, though, are the features Dropbox has built-in for cataloguing and organising. The app can read PDFs, Word documents and HTML files natively, without having to launch another app. Your "recipes" folder gets organised in alphabetical order, and you can quickly mark down your culinary successes with a star for quick access later. Want to share a recipe with a dinner guest who especially loved it? Email it right from Dropbox, and they'll get your copy of it, not a link they'll have a hard time searching for later.
My wife maintains a fairly rich collection of recipes grabbed from all sorts of places in a desktop folder, so this is just an observation I made while hooking it up to Dropbox last night. If you've got another recommendation for how to make an iPod touch or iPhone into a great kitchen assistant, drop it in the comments.