http://www.neilslade.com/Papers/how.html
If you think i'm wrong then so be it. I'm not saying that you have to agree with me.
I'm doing an Honors Double Major in Psychology and Sociology...the Psych part is the important one here. In particular, I've taken Cognitive Psychology (study of the brain) and Neuropsychology classes, and the professors I've had (along with the textbooks, along with the actual scientific research) have pointed to the fact (<--fact, not opinion) that we do not use 10% of our brain, or any low figure like that.
As has been mentioned, we do indeed use all of (or most of) our brain. However, again as pointed out, we only use a portion of it at any one time (although, even that portion is over 10%). The myth that we only use 10% of our brain came about before we could properly study the brain (the technology only came about in the past 20-30 years or so), but now that we have the technology to study the brain properly, we know that we use every part of our brain.
Also, although nothing is 100% in science (or anything, really), it's commonly accepted that we don't have an "infinite potential". There are genetic boundaries in place, as well as physical boundaries (the actual structure of the brain). Don't get me wrong, the brain is an incredible thing--the elasticity of it (the ability for other parts of the brain to take on dual roles when one part gets damaged early on) is beyond amazing. But, in order for us to do more things, we'll need to keep evolving and grow a new part to our brain, since every part of our brain as it currently stands is spoken for--there's no telekinesis portion, sadly.
With that said, there's still a lot about our brain that we don't know, but that type of stuff is more along the lines of not knowing the exact mechanism for coding things into memory (we know
where we store stuff for both long and short term memory, but the
how is a little fuzzy--there are hypotheses, but nothing overwhelmingly concrete), how exactly we interpret visual inputs (again, there are hypotheses--incredibly detailed and sophisticated hypotheses, mind you--but nothing is concrete), etc.
But, we've got the brain pretty well mapped out. What each part of the brain is for is not a mystery, like it once was. Now we're just working on specifics.
And that's just
my (slightly educated) opinion. Believe me (and science) if ya like, or not. Doesn't hurt me at all.
Edit: PS, that source made me "LOL"...you should cite scholarly journals when making a scientific claim if you're going to cite anything...internet articles are a laughable waste of time at best, and can spread scarily wrong information that people will believe at worst. True story--Dr. Johnson McHonesty told me on his website...I'd link you, but his page recently went down.

You should have stuck to keeping it just an opinion. =/
Also, the "only use 10% of our brain" myth, I suppose, can be pretty good for a line in a mentalism routine. I wouldn't use it personally, but it definitely works. I prefer to take actual facts, and slightly twist those.
