I always thought this. When I got my MacBook back in 06, all the other laptops I saw had at least 3 USB ports spread on both sides of the laptop.
However, I never needed more than one or two on the go for a USB stick and maybe my iPod/iPhone cable. Nothing else is necessary for me when I'm out.
When I get home its a different story though. My powered Dock gets plugged in with its 5 USB ports and top-loading iPod/iPhone dock. I have 3 USB external hard drives with music, TV series, films etc and a spare that doesn't get plugged in "just in case." Plus my Soundsticks that use the USB port and logitech wireless mouse charger/receiver. That still leaves me with the FireWire port spare for the MyBook 300GB that is currently plugged into my Cube, and a USB port for any pen drives I can put in the machine when I'm in a hurry.
I would recommend using a FW external drive, although they are a little more expensive than a USB one, that is a 3rd port if you need it.
Or you could use a Bluetooth keyboard and mouse and save those ports altogether.
But if you use your laptop for any extended period of time as your main computer, I'd definitely recommend a powered USB hub, I'm very happy with mine!
David