homerjward said:
some hubs come with a power brick in case the devices run out of power.
USB requires that the current being drawn over a single USB connection be under 500mA (high-power USB). Bus-powered hubs - hubs that draw power over their USB connection - therefore can't offer more than that in total since they're drawing their power from the computer over a single USB port. So bus-powered hubs generally limit the current draw to 100mA per port (called low-power USB). Devices like the iPod, though, want quite a bit more than 100mA - so they won't work reliably on a bus-powered hub.
A hub that has its own power supply is called "self powered". They can offer up to the full 500mA on each USB port. If you want to be able to plug anything into the hub without worrying about its power requirements, you want a self powered hub.
Thing is, though, I've had trouble with USB hubs; at least on Windows (I've never needed more than the two available ports on my Powerbook). It seems to be related to the power-saving features of the OS. Devices get plugged in, get recognized, and work fine... until they've been idle for a length of time. Then they seem to just get lost.
Main reason I see for using a hub, though, is when you've got a desktop machine with all the USB ports in back.
😀 (I've never understood that design) The ports on a Powerbook are easy to get to, so going plug-and-play isn't a big deal.