Apple's iOS 4 (iPhone OS 4) added an important missing feature: a way to save your notes online. If you add an IMAP mail account like Gmail or Yahoo Mail and enable the notes feature, you can create notes that are saved to your email account.
For Gmail, Apple creates a label called Notes and saves the notes created in the Gmail section to your Gmail account. The notes can only be edited from an iPhone or iPod Touch and the changed are reflected in Gmail.
Some other new iOS 4 features that should be useful for Google users: Google Suggest in Safari's search box, an option to search the Web in Spotlight and the ability to add multiple Exchange accounts.