Internet Explorer 8: Is "InPrivate browsing" really private?

We've all seen the adverts on TV and splashed on the web, telling us we can hide our browsing habits, by utilizing IE8' "InPrivate" browsing facility. But how private is this mode really? Will it for example, stop a suspicious spouse from spying on you? Will it prevent your employer or IT dept, finding out you're going to Facebook when you're meant to be working?You'd be forgiven if you'd said