Well, it can be customized to show just about any information you want. Sometimes, you'll need other software running to feed the data to rainmeter, though.
My skin features average CPU use, frequency and temperature. RAM, HDD and network use. Battery level. Weather forecasts:https://dl.dropboxusercontent.com/u/7904468/Desktop/screen2.jpg
Making your own skin takes some time and skill, but there are hundreds of premade skins out there, too.