Quick switching between wireframe and normal view

 I do not think there is a "default" key for it, but you can easily assign one -

Click on the view menu, once open right click and select "Customize" then "View Menu"

then "Add New Command"  look in the drop down box, ( next to the binoculars :) find "View" Find your command (wire, enhanced etc...), select it and open the "Shortcut Keys" ( center top tab )

Move your cursor into the assign box and press whatever key you want to assign, remember to click the assign button next to it when you are done,

Click OK at the bottom and yer done! 

~Muts