See the latest version on the documentation wiki.
I found it convenient to be able to power the Web Platform using my iPhone USB charger and a normal USB cable. It is also convenient when presenting the board to friends and powering it using their computer. Therefore I soldered a pluggable (via two DIL socket pins) connection from the USB power to the 3.3 volts regulator (picture attached). I measured the consumed current which is about 200 mA, so when powering no additional hardware with the Web Platform it should be ok for most USB ports.
In a future revision of the board maybe a switch could be added to choose the power source, similar to the solution on the Seeeduino.
You can buy an assembled web platform for $40, including worldwide shipping.