I think the left side is more suited for backspace. Which is how my Compaq keyboard is setup - the key is physically divided into two. Perhaps the spacebar is

I think the left side is more suited for backspace. Which is how my Compaq keyboard is setup - the key is physically divided into two. Perhaps the spacebar is just too big, and could be divided better into other modifiers. My left thumb is usually wasted (though not on a Mac, where the thumb can easily reach the Command key.) Some people however - seem to alternate thumbs on the spacebar - or rather use the other hands thumb to the hand that just typed a character. I personally always use the right thumb to space.