I've just uploaded a patch I've written for PHPWiki, to the FreeSide wiki, that fixes PHPWiki 1.3.x's munged RSS output when using gzip compression.
The error occurs when output is compressed with gzip so that clients that support compression will grab the smaller, more bandwidth friendly version, and clients that don't will grab an uncompressed version; the output of PHPWiki is garbled and normally results in an error signal when the output is RSS or XML other than XHTML (or flat CSS), probably because of PHPWiki's integrated gzip library (I presume used for portability) and stream handling, some sort of conversion is being used on the output before compressed and sending to Apache's buffer.
The simple hack-fix was to check for RSS, or any other non-standard output, and disable inbuilt gzip compression, and then enable PHP's own output buffering with gzip compression.
I've also made use of the well known 404 redirect hack in order to implement URL/page-to-wiki-node function, by which typing any 'freeside.co.uk/SomePageHere address will take you to the corresponding 'freeside.co.uk/index.php/SomePageHere node; mainly because I, and a few others, kept typing this former address type when we meant the latter (and it just makes sense); you may recognise this system from the PHP website, which will take you to any match manual entry, or provide a list of possible matches when no matching entry is found (or several are found).