Frenzy author here.

If you were the last person to reply in a conversation you can delete your own reply by holding down the option key. The reply button will then change to a delete button. There is still currently no way to delete an entire conversation though.

I was possibly thinking of adding the ability to archive items you've seen already so they don't show again.

Regarding point 2 - thanks, good thinking. I will definitely need to make this clearer as many are still confused as to how to actually share things. Most try and drag files into the message text field or onto the menu item which is not yet supported.

I'm glad you like it :)