FOR those whose comments and feeds are not working change the PERMISSION OF THE .HTACCESS FILE IN YOU HOST TO 0777 OR 0755.
that should solve your problem.
thats not any kind of solution for anything other than when updating or changing your permalink settings.
Furthermore, you are telling people to assign executable permissions to a file thats NEVER executable.
this is the correct info:
when needing to have wordpress write to your .htaccess, you can chmod your .htaccess to 666.
after wordpress is done writing to the .htaccess, the permissions for your .htaccess need to be changed back to 644.
NOT doing so, leaves that file as world-writable and is a HUGE security risk.