Gnome3 is revolutionary. But to enjoy its benefits, I had to exercise my zen side and let many old habits behind. I decided to give it a try. I'm liking it.
But even liking Gnome3, I was missing System-Monitor applet. But now I have it. :-)
I followed Matthew Casperson's post and added just some little steps:
After following the steps described on Matthew Casperson's post:
$ mkdir ~/bin
$ cd ~/bin
$ ln -s ~/git_projects/gnome-shell-system-monitor-applet/system-monitor-applet-config.py system-monitor-applet-config
Those steps will enable you to call "Preferences" on the applet icon.
I would also recommend reading other Matthew Casperson's post: Gnome 3 Tips and Tricks