Command that Works in Terminal Not Running as Launch Agent

Question

Trying to run the following command as a Launch Agent (OS X 10.7):
/usr/bin/find /Users/username/Documents/Dropbox/Public -type f -mtime +2 -print0 | xargs -0 rm -r
Created a plist file (reproduced below) and saved to ~/Library/Launch Agents, but the command isn't executed either at the specified time or when the agent is loaded via launchctl.
If I change the command to a simple Applescript test:
osascript -e 'tell Application "Finder" to display dialog "hello"'
It runs correctly as a launch agent when loaded and as the specified time
Which means there's something wrong with the first command (find). But the command runs as written when executed manually in the terminal.
Suggestions? Thanks.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
          <key>Label</key>
          <string>com.username.clean_dropbox</string>
          <key>ProgramArguments</key>
          <array>
                    <string>/usr/bin/find</string>
                    <string>/Users/username/Documents/Dropbox/Public</string>
                    <string>-type</string>
                    <string>f</string>
                    <string>-mtime</string>
                    <string>+2</string>
                    <string>-print0</string>
                    <string>|</string>
                    <string>xargs</string>
                    <string>-0</string>
                    <string>rm</string>
                    <string>-r</string>
          </array>
          <key>RunAtLoad</key>
          <true/>
          <key>StartCalendarInterval</key>
          <dict>
                    <key>Hour</key>
                    <integer>17</integer>
                    <key>Minute</key>
                    <integer>45</integer>
          </dict>
</dict>
</plist>

Answer 1

Since your pipe is essentially just passing the find matches to rm, you can achieve the same result using find's -delete switch:
/usr/bin/find /Users/username/Documents/Dropbox/Public -type f -mtime +2 -delete