9800 GTX+...

[ZenOne]

does it take up 2 PCI-E slots or only one and but simply big?

 

[Schadenfroh]

Some (if not all) take up two slots

 

[vj8usa]

It only connects to one slot, but it physically blocks the adjacent slot (PCIe x1 on a lot of boards) with its cooler. It'll also use up the adjacent slot's backplate.

 

[Keysplayr]

It only takes up one PCI-e Slot.