Once a user has been to the main page of a website or microsite why keep taking up valuable screen real-estate by showing the side navigation bar. Might a better way be to attach a panel to the left of the browser window with a vertical label of 'Menu' or 'Navigiation' that when the user hovers over it, use css to display those hidden options?

This should work OK as the user's mind is ready in the 'context' of the microsite. However, the user might have bookmarked the page and would then be coming in 'cold' to the page at a later time. The question is then whether the trade off is worth the cost of the user's mind not being primed enough to accept the menu options being hidden in a flyout menu?