I'm running a 2011 Macbook Pro with 2.7 mhz and 8 meg of ram. I would say that I'm seeing a lot more "wait wheels" than previously. I do like some of the changes such as discrete browsing, but its coming at the price of a slower machine.
Mine's 2.4mhz with 8 meg ram as well, but I changed the hard drive to an 500 gb SSD and it really helps. I don't seem to have any problems with speed now Yosemite is installed.