I've been using this applet on 3 different machines. All of them had a memory leak regarding the 'polkitd' process. It's memory usage slowly but steadily increased. Since I don't shutdown my computer but rather suspend it, after a couple days, polkitd's memory usage will be around 500MB and I have to restart my system to re-claim the memory.
After seeing this bug report I've noticed the problem was caused by this applet. Removing this applet solved the issue.