The latest version of Microsoft Office Excel till date i.e. Excel 2007. The extension of files created or edited with Excel 2007 are saved as .xlsx files. This kind of file is not supported by the earlier versions of Microsoft Excel i.e. by Excel 2003. This kind of file was also not supported by Google docs and you would have to convert them into older file formats. But recently they have added a feature letting you to upload Excel 2007 files.
Now when you upload a .xlsx file in Google Spreadsheets, your document is readily accepted and can be quickly edited. Google Docs can import all the cell data, formulas etc. The formatting is not preserved by the way.
Google Spreadsheets supports file extensions like .xls, .xlsx, .ods, .csv, .tsv, .txt, .tsb. The ability for uploading Excel 2007 files in google docs doesn’t mean that you can also upload Word 2007 files. Google docs has still to work on this as currently Google Documents only supports uploading of .txt, .doc and .rtf extensions. .docx is still not supported and third party applications should be relied upon to upload such files in Google Docs.
So, you can now have a greater flexibility for your Spreadsheets documents and needn’t worry about converting your Excel 2007 files to older version.