Changing from ms office to iWork?

I'm considering going from ms office to iWork, but I have a major question.

How easily can office users open a document in Pages, Numbers and Keynotes?

I'm not too worried about converting my docx documents, but I often have to email documents to ms users and it is paramount that these people can open and work with the documents I send them.

Any pros and cons for converting to iWork?

Thanks

Charlotte