Ever since my upgrade to Natty Narwhal, applets (e.g, clock, weather indicator, indicator applet.) will crash the second I reach the desktop after logging into Ubuntu Classic. Which one is rather random, but it's always at least one or more of those. Is this a known bug, or is there something wrong with my system?
It seems this bug has been reported before: https://bugs.launchpad.net/ubuntu/+source/indicator-applet/+bug/537383
Your information seems to be useful since the bug was closed due to lack of information (given the number of people who reported themselves as affected I don't believe this should have happened).
You could try to reinstall the packages:
sudo apt-get install --reinstall indicator-applet indicator-messages indicator-sound