There is no way out of the box to hide the Quick Launch and the Tree View navigation in SharePoint 2010. Let´s say you have a team site and you really want to use the full width of the home page of this team site. How to do this?
The easiest way is to use the old school CEWP trick that worked even back in 2003, just add a the Web Part that now has the name Content Editor and add the following text in the HTML Source mode:


/*--Hide Quick Launch --*/
#s4-leftpanel{
display:none
}
.s4-ca{
margin-left:0px
}

You can also download and import this as a .dwp from here if you like.

The Master page that includes this navigation control does not longer have a table structure as it had in SharePoint 2007, which gives a cleaner and a well-formed markup HTML. The DIV elements in the master are floated to each other and have their positions defined by margins or a width, this is why I had to set the margin to zero for the s4-ca class, the wrapper for the content in the page. The value for the left panel ID can be set to not be displayed.