Really? I use it on variety of Macs (2008 Mac Pro, 2011 27'' iMac, 2007 24'' iMac, 2008 Aluminum Macbook, 2011 17'' Macbook Pro) and it runs smoothly and doesn't use much CPU at all on any of them. During video calls it will use more CPU but that's somewhat expected (Factime video calls do too).
It beats Safari and Chrome by CPU time and packets sent by orders of magnitude. Of course Chrome and Safari processes are separated nowadays, but still they do have some central stuff.
