[CentOS] General question about understanding PCI passthrough

Greetings -

I saw Andrew Holway's post yesterday referencing using PCI passthrough as a 
solution to someone else's issue.  Not being familiar with it, the post made 
me look into it more to see if it is something to use for my setup.  From my 
research on the web, I have two questions to make sure I understand how PCI 
passthrough works.

1.  If you use PCI passthrough on a graphics card to allow a virtual guest 
direct access to the graphics card for it use, does the host still have use 
of the graphics card also?

2.  Or, once you pass it to the guest, the host can then no longer use it 
and has to rely on base level motherboard graphics?  It looks from my 
reading that using PCI passthrough you can make the graphics card available 
to multiple guest simultaneously, but it seemed to imply that the host could 
no longer use it.

With the box that I am configuring, I was planning on installing Linux Mint 
(Cinnamon Desktop) as my kvm host, then installing Win7 as a virtual guest. 
Since I use some mapping software in Win7 it would be nice to be able to use 
the graphics card via PCI passthrough, but not at the expense of loosing it 
from the Mint Cinnamon Desktop.  However if multiple kvm guests can use the 
graphics card simultaneously (but the host can not), the maybe I should use 
CentOS as a very basic host and then make both Mint and Win7 guests.

Jeff Boyce
Meridian Environmental