Small, light, low-cost netbooks like the Acer Aspire One and ASUS Eee PC may be all the rage - but they may not be the ultimate portable computer.  That honor belongs to the ubiquitous USB drive - powered either by flash memory or by microSD cards.  At a fraction of the size, weighing almost nothing, and costing less than $2 per GB of storage, the devices can be loaded with excellent free software and with an available USB port on a nearby computer make the ultimate portable PC.