(For PC games I stick with the arrow keys, personally.)
Yuck. I remember when I first started PC gaming years ago I used the arrow keys, but considering how nearby keys like Q, E, F, C, X etc also get used by default, it's highly inefficient.
^Don't worry about it. 'WASD' will very quickly become second nature. The only tricky part is the space button, which for some reason Bioware decided to assign about 50 different situational functions to. It can make running away, diving and getting in and out of cover a bit of a toss up as to which you intend to do and what you'll actually do.
*Shepard runs up to a button on a wall to press it, proceeds to dive roll into the wall*