Had a quick look. None of this looks like features for power users. How are "spaces" different than having multiple open windows?
However, listing this as the only difference when asked make it sound like you're selling "spaces" as only a slight performance improvement and nothing else.
However, that aside, it makes no difference whether you have a window, tab, or "space".
- JavaScript on one page dragging down all tabs
- Memory leaks
- JavaScript exploits that crossed tabs
And so on.
Multi process browsing is fantastic.
So all we really won was performance regressions (the IPC is expensive) and significantly increased resource consumption.