4 PCI cards for me, total available for use is 5.
SCSI card, NIC, Sound Card, TV Tuner.
I also use the 1st PCI slot (next to AGP) to help avoid any motherboard IRQ conflicts, still stuck in my head from Win98 days. The last open PCI slot would be a tough fit since it has to go between a the TV tuner and another card.
If I did have the NV35 taking 2 slots, it kind of wouldn't be a problem, but then again if I wanted to get another PCI card I would be stuck. But what PCI card would I need down the road? Firewire? Serial ATA? etc.... Don't know, I feel like I got everything that I use covered now..... but if a new technology comes out and requires a PCI card for the people already near to full then the 2 slot video card would pose a problem for me.
For me, I don't much care for a video card taking up two slots, so I'll probably avoid nVidia 2 slot video cards for the time being until I can free up some space, like with integrated NIC, sound, etc.