Because of this I still prefer Luna to Freya.... maybe I'm just used to Luna. Hell, I find Luna's login screen more elegant and inviting.
Had a lab I needed to image, very low spec PCs (XP was bearable). I tried Ubuntu 14.04 but those PCs suffered. Threw Mint XFCE at them and they capably handled workloads. Funnily enough, when I tried Luna afterwards, they felt like newly purchased PCs. Freya.... performance is suffering slightly, now they're equivalent to Mint XFCE's level. And its not specific to those lab pcs, even on my Sandybridge i5 lappy the perf difference between Luna and Freya is apparent. It could just be that Freya's a RC right now iirc.
Well, doesn't matter anyway, I need to be on the latest LTS as I've less time for tinkering.
Not sure what freya uses but this could also be related to the gtk toolkit, gtk3 has put on more weight with time.
