This Tenth Circuit case, beginning on page 20. The court offers a nice standard for what inferences are permissible under 701 and when they are grounded in expertise requiring qualification under 702. At issue was a company CEO's testimony about lost profits for calculating damages in a breach-of-contract case and whether it was based on his observations and knowledge as CEO (and thus constitutes lay opinion) or whether it relied on more complex math, experience, and expertise (and thus his qualification as an expert).
It is worth noting that similar problems arise with law-enforcement testimony. Officers go back and forth between lay and expert testimony without expert qualification, often without the court closely monitoring this movement.
