The resume feature is a life saver for people who often don't remember to save work (kids).  However, I agree with you that it can be embarrassing and annoying when using Safari. I suggest you disable it.  Unfortunately, it's a global system preference.

You can do that here: http://cl.ly/1D3n0g3Z2V0v1P0C292T

I never used spaces so I can't comment on that. However, I do like full screen mode which leverages the spaces concept.

The OS introduces quite a few changes.  Some I love, some I accept.