The Microsoft Office spellchecker is a very good product, and I suspect you might be thinking, "what's the but", and yes there's a but.
There are thousands of words in the Microsoft dictionary which can be spelt two and perhaps more ways. Whilst the variations are generally considered correct, most people consider the secondary spelling variations to be incorrect and that can detract from your writing. Worse though, is if you include material you've copied and paste you could easily introduce inconsistent spelling into your document, where you use the two different spelling variations and that is always considered incorrect. For example to use both organise and organize in the one document is considered incorrect, but is quite possible with Microsoft Office. Many people also flip flop between ise and ize spelling variations in a document not really knowing which spelling variation they should use and going on gut feel. This detracts from the quality of their document or writing which reduces the impact of the message the writing aims to get across.
If you've ever sat in a Microsoft seminar to see them use the spelling license for their software in Australia, you'll realise how important spelling is. The message Microsoft sends to an Australian audience is they don't care enough to localise their product, or even the presenters slides for the audience and that severly reduces their perceived sincerity.
In addition Microsoft Office includes words which are incorrect for Australian usage. The most obvious example is mom.
To overcome these issues I've provided an Exclude file you can install which will mark over 2,400 words as incorrectly spelt. The words are either words which shouldn't be in the Microsoft spellcheck dictionary or they are a secondary spelling variation.
If you prefer consistent spelling in your documents, if you prefer to use the preferred Australian English spelling in your documents and emails, if you really value your audience, then my Microsoft Exclude file is a great investment for you.
You can obtain the Microsoft Exclude file using this link.