two questions: why USB2 instead of USB3 and will there be a multi-nic version at some point?

Thanks for all the info.  I didn't realize that USB3 was so cumbersome to implement.  As to the thoughts on multiple nics, I understand the desire for cheap hardware and to keep the size down, but I don't understand the comments about multi port hubs and cheap ethernet adaptors.  Having a multiport ethernet hub solves nothing when that hub is connected to a single nic since hubs, by design, are dumb and don't understand routing rules (and if you mean a multiport USB hub, I don't know how you would use that as a multinic ethernet device at all).  All traffic on every port of an ethernet hub (and I'm speaking strictly of multiport hubs, not multiport routers/switches) is seen by every other port on that hub and so it's impossible to run multiple ethernet networks on a hub (and defeats the purpose of my thought of having one nice little inexpensive card as a firewall device; adding extra hardware now increases the cost to the point where you might as well pick up, as another poster pointed out, a cheap router flashed with open-wrt or tomato and forgo the PI completely).  You *could*, as another poster mentioned, purchase a USB nic and have two nics that way, which is a possibility but then one of the USB ports is now used as a dedicated port for routing (not an issue if you have a USB hub to connect keyboard and mouse to the other USB port).  Anyway, this discussion has been very informative for me and I appreciate all of the comments.

No, I did mean a USB2.0 hub and USB2.0 ethernet adaptor.  Both are common and cheap.

This is actually how the Model B works internally.  The system-on-a-chip provides one USB2.0 port.  A USB2.0 hub and ethernet adaptor are soldered on to the board.  USB2 is the fastest bus provided by the chip, AFAIK.

All add-on devices have to be USB and share that single 480Mbps half-duplex connection.  That means you have just barely enough bandwidth to max out two full-duplex 10/100 ethernet adaptors.  If you have fast large storage on your USB as well, that would be a point of congestion (but only if all traffic, including hard drive activity, is heavily bidirectional)

No, I did mean a USB2.0 hub and USB2.0 ethernet adaptor.  Both are common and cheap.

This is actually how the Model B works internally.  The system-on-a-chip provides one USB2.0 port.  A USB2.0 hub and ethernet adaptor are soldered on to the board.  USB2 is the fastest bus provided by the chip, AFAIK.

All add-on devices have to be USB and share that single 480Mbps half-duplex connection.  That means you have just barely enough bandwidth to max out two full-duplex 10/100 ethernet adaptors.  If you have fast large storage on your USB as well, that would be a point of congestion (but only if all traffic, including hard drive activity, is heavily bidirectional)