Reporting Services rendering to non-Windows clients

[No one]

I have an ASP.Net control written in C# that renders reports via
Reporting Services through the Response.BinraryWrite method. I do set
the content encoding and MIME types as per that is returned from the RS
object's render method. Browsers on Windows machines (IE, Netscape 7
and Firefox) all see the correct MIME type, typically Excel, and show
the resulting report. Browsers on Macs and Linux, however, see the
correct MIME type, but only render gibberish. Is this normal behavior,
or should these not render properly on those platforms as well?