It works great - but a couple of times my accountant has said that he couldn't read the files. I don't know whether this is a problem from sending floppies in the post or him not knowing how to use WinZip or what.

If you keep to simple stuff it will be fine. However if you regularly need to exchange complicated MS Office files with other MSOffice users then consider coughing up the dosh. (And this is me - Mr Open Source - saying that).