Keep Boxee running.

net.spy.boxee.plist

<!DOCTYPE plist PUBLIC -//Apple Computer//DTD PLIST 1.0//EN
          http://www.apple.com/DTDs/PropertyList-1.0.dtd >
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>net.spy.boxee</string>
    <key>ProgramArguments</key>
    <array>
      <string>/usr/bin/open</string>
      <string>-W</string>
      <string>/Applications/Boxee.app</string>
    </array>
    <key>KeepAlive</key>
    <true/>
    <key>RunAtLoad</key>
    <true/>
  </dict>
</plist>