Very glad you posted! I would also add checking with each new project, especially if you are using a foot that has a metal guide piece on it.
My preference is usually for my Janome's optional 1/8-1/4 clear foot with guide, vs. the O2 solid metal foot with guide. Something didn't look quite right the last time I put the clear foot on the machine and when I checked my seam width, it was more than a scant over 1/4" (it had always been a perfect scant less). Looking more closely, it seems either the plastic ridge that holds the guide is wearing OR the guide has weakened and bent open a little, because it's no longer perfectly upright and flush against the side of the foot. Time to replace it!
Michelle