I was experiencing some serious network latency issues from my iMac to a networked Mac mini and a FireWire 800 connected storage array tonight and discovered something very shocking. It appears that if you have a window open containing a QuickTime-compatible video library, Lion wants to cache a portion (or possibly the whole file) for quick access using Quick Look. This becomes problematic when you have a large video library and even more problematic when the library is on a network share. My LAN utilization skyrockets to 100% of its capability (100BaseT) and stays there for at least 45 minutes, possibly longer. I closed the window before I could see if it would stop or keep on cycling. As soon as the window is closed, the QTKitServer process and the network bandwidth drops to normal levels. I recently switched from a Netgear gateway to a more powerful pfSense setup because the Netgear kept flaking out on me. With all this traffic, I now know why. Is anyone else able to duplicate this problem with Snow Leopard? All you need is a folder full of video content on a network share, in a format that can be previewed with Quick Look (m4v, mp4, etc). Set the folder to list view and sit back and watch your network traffic in Activity Monitor.