<p>I've come across the problem where Excel will not play nice with UTF-8 encoded CSV files. See this <a href="https://stackoverflow.com/questions/155097/microsoft-excel-mangles-diacritics-in-csv-files">related question</a> on Stack Overflow.</p>

<p>I've followed the solution of exporting as UTF-16, however it seems that with UTF-16, the comma character doesn't work as a delimiter, only the tab character.</p>

<p>However I can't find anywhere what the correct filename and mime-type should be for tab-delimited files. I found somewhere stating that it was application/vnd.ms-excel and xls. This works ok for Excel 2003 but 2007 does not approve.</p>

<p>So what should it be?</p>

For tab-delimited files,
http://www.rfc-editor.org/rfc/rfc4180.txt
mentions 'text/tab-separated-values'.
That format is (sparsely) described at
http://www.iana.org/assignments/media-types/text/tab-separated-values
.
More info can be found at :
http://www.cs.tut.fi/~jkorpela/TSV.html
I hope this helps?