I too only press my seams open when the block calls for it (lots of seams coming together in 1 point) or on a One Block Wonder.
NOTE: When pressing seams open you really need to shorten your stitch length, on my Bernina I always use a 2 which I believe is 12 stitches to the inch. Most machines (new) default to about 10. Also think about how you are going to quilt it - I haven't tried it but a lot of people say to NOT stitch in the ditch on seams pressed open. When you think about it that makes sense - you are going to be stitching into stitches and have the chance that you could be breaking those that are holding your pieceing together. Of course that is if unlike me you actually hit a ditch.