Who should file an 83(b) form?

This should be filed by founders or employees receiving restricted stock with a vesting schedule. Essentially, individuals who want to pay income tax on the current low value of their stock, instead of the (potentially much higher) value as it vests over time. If you don't file an 83(b) you'll owe income tax each time a portion of your stock vests, based on its then-current value.