Rulers - When the numbers/lines wear off
Cutting Mats - Every 5 or 6 years or so
Rotary cutters - When they break. I sew a LOT, so I'm hard on them
Rotary blades - When they start skipping more than a couple of times per WOF cut
Pins - When they're too bent to straighten back out, or when the "head" comes off
Needles - My machine makes a "whumping" sound when it needs a new needle. I don't hand-sew enough to wear regular needles out.
Chairs - Not often enough. My current chair is an office chair with a pillow on it. I wore the cushion out.
Sewing M achines - When it starts causing more frustrations than it's worth, or when I happen across a really good deal on one I like.
Sc issors - Every couple of years for "everyday" sc issors. I inherited my Granny's Ginghers, which I'll never replace. <3
Seam Rippers - When they get dull or when they sprout legs and walk off.