In general, and understanding the answer may vary by manufacturer and model (and driver, and...), in consumer-grade workstations with integrated NICs, does the NIC rely on the CPU for a lot of help (as is typically the case with a USB controller, for instance), or is it fairly intelligent and capable on its own (like, say, the typical Firewire controller)? Or is the question too general to answer? (If it matters, you can assume Linux.)

Background: I'm looking at connecting a device (digital television capture) that will be delivering ~20-50 Mbit/sec of data to a somewhat under-powered workstation. I can get a USB 2 High-speed device, or a network-attached device, and am interested in avoiding impacting the CPU where possible. Obviously, if it's a 100Mbit NIC, that's roughly half its theoretical inbound bandwidth, whereas it's only roughly a tenth of the 480 Mbit/second the USB 2 "High Speed" interface. But if the latter requires a lot of CPU support and the former doesn't...