Uhhm, the brain isn't just a wetware version of a silicon-based computer like an Intel chip. What it means to "use" the brain is almost certainly not what it means to "use" a computer. It isn't just a matter of rationalizing your programs and the processing mechanisms of the CPU - like multi-threading and out-of-order processing - to try and use all of the clock cycles of the cpu for doing something - i.e., reducing system idle time.
For example, as far as appears, the brain integrates both processing functions and data storage functions. Computers do not do that; even with on-chip cache memory there is still a distinct difference between the CPU logic proper and the memory. Furthermore, unless your computer is running a RAID disk system, physical damage to part of a disk makes it virtually impossible to access any files that were partly stored on the damaged area. Certainly, a silicon-based computer cannot repair the damage done to its hard drive. By contrast human memory displays certain aspects of holograms, in which each piece of a broken hologram can still provide a perspective view of the entire hologram.
Also, the belief that only 10% of the mammalian brain is being used at any given time is rather an insult to the creativity Mother Nature displays, in which almost every part - certainly the most important parts - of an organism is used and where significant parts that lose their primary function are repurposed for another use. The human brain is, actually, a good demonstration of that: when a portion of the brain is cut off from the part of the body it was originally connected to, surrounding areas of the brain will slowly take over the unused portions. This is the source of the so-called phantom limb phenomenon, in which an amputee still feels that they have the limb they lost. That sensation is, apparently, caused by other parts of the brain beginning to use the neurons that until then had been used to map the limb that was amputated.
In other words, nature is rarely so wasteful with valuable resources, and the mammalian brain is most definitely a valuable resource, considering how much energy it takes to run the thing.