I am in the process of shopping around for an external SSD which runs on USB2 (yes such things exist) of around 32gb or so. I know that the SSD would totally choke the USB2 connection, but even with only a 480mbps bus, the read/write/random access speed would be amazing compared to the SD card, and would give performance comparable to a decent 7200rpm HDD. it would also mean that swapping to the drive would probably be fast..
(actually... thats another thought. how fast is the memory on the-r-pi? i know that modern ssds are getting to the point where they are almost as fast as pc66 ram.. and i am guessing that putting a decent ssd on there will be almost similiar to extending the ram by many GB, albeit at a much lower speed. setting swappines up to be very high might turn this into a very fast little computer, but i digress)
One thing I worry about though is the sustained transfer capability and the bus sharing abilities of R-pi. I plan on having a USB hub, with wireless keyboard/mouse/wifi dongle/ssd on it. is the usb port capable of handling all 3 of these things without slowing down hdd access everytime i move the mouse? and if i was, say, copying an 8gb file from the sd to the hdd, would that jam the port up and make input/network stuff lag? using the network port instead of wifi is a definite posibility if this is an issue.
TL;DR: will the usb work with a mouse/keyboard when a sustained transfer of 480mbps is taking place? or will it cause lag?