Yes I use it heavily. I track my accounts as you do so I don't have to log into anything. I put in all my trades and notes in there as well. I also track quite a few ETFs, mutual funds and stocks and compare their performance for the past 1-12 months. I also track different strategies that I 'paper trade' to see how they are doing. I have some momentum strategies, Joel Greenblatt's Magic Formula strat, Mebane Faber's global CAPE investing, among others.
I love the ease of use and the real-time data. I know it's possible to do the same in Excel with yahoo finance, but the Google functions are so much easier to learn.