Deprecated features in Excel 2007: (from, accessed 28.11.2007)“Before jumping to the list of which features are being deprecated or removed, let me say that we never make decisions lightly about removing functionality that has been in the product.  We rarely remove functionality and strive for backwards compatibility with every version.  When we do make changes to functionality that has been in the product we do so when we believe it will be a benefit to the majority of our customers by helping us to make forward progress… Historically Excel has supported many different data formats.  We have determined that a number of these older formats are seldom, if ever used.  We are removing support for some file types to allow us to devote more of our efforts towards the file formats that are being used.  Theses formats are being deprecated in 2 ways.  For the set of file formats with the lowest usage, we will be discontinuing support for opening and saving of these formats.  For the second set that has some minimal usage, we will support loading the files in Excel 2007 to allow you to save them in a newer format.”

The formats which Excel 2007 cannot even open (let alone save) include WK1 and WK4 (1-2-3 formats) and Microsoft Excel Chart (.xlc). Older versions of Excel, such as Excel 2.0, can be opened but any editing would result in the files being updated to more recent ones. Discussion on the blog suggests that there’s a lot of WK* files out there, none now easily openable.