Yes - look at the link that Paper Princess included. There is more to a perfect quarter inch seam than the actual seam - because you are using the quarter inch seam in hopes of getting consistent and correct measurements on the block - you need to measure the pressed block. Thread choice and pressing skill can have an effect on your finished project.
I use the yellow Perkins Perfect Piecing Seam Guide to set my machine - I use a stack of 1/4 inch tape as the guide to run my fabric along - I find that if my guide is not taped down to my machine, then the fabric is just as likely to move underneath it.
Deb Karasik has created a great seam gauge and guide that I am coveting - especially after seeing her use it in class.
Cheers, K