Spellcheck within a web form is very handy, but potentially annoying if you favour Australian spellings over the US alternatives. If you're a Google Chrome user, there is an option to set up Australian spell-checking instead.
I'll confess I hadn't realised that Chrome had this option until I saw it praised on Twitter. To enable it, click the Chrome wrench icon, select Options, select Under the Hood, scroll down to Change font and language settings, and choose the Languages tab. In here, you can select English (Australia) for your spellcheck, and also set it as your default language for reading pages.
While you can change most language options to Australian English, the closest you can get for the actual interface language is UK English. (Firefox and Internet Explorer sport similar options that are somewhat easier to find, though I can't recall ever specifically enabling these in Firefox, so I'm guessing that my current setting of EN-AU was picked up from other system settings.)