Yeah those get me too; If it weren't for all those petty errors I could probably type 150 consistently.
I guess you are as strong as your weakest link and my weakest links are the obscure letters or rather the letters in obscure places (Q, Z, X) and numbers (never fully practiced learning them but in theory know how to type them (the top row of numbers, not the number pad).
Also symbols get me a little bit.