Whenever I want to reply to an iCal event it opens up Mail.app to send the response. I don't use Mail.app and use Sparrow instead. Sparrow is set as the default mail client but that doesn't seem to make any difference. Is there any way to make iCal not open up Mail.app and use "Insert any other mail client here" instead
Theres a pre written apple script solution for this and fairly easy instructions that any apple script novice should be able to follow. You can find the download and instructions here.