On Jetstar, pretty much every time (in combination with my main carry-on for weight). Not an airline to roll the dice with!
Less frequently but on occasion: Singapore Airlines out of Sydney, especially after the turbulence incident a few years ago where luggage fell out of the overhead and caused major injuries. Check was mainly for potentially overweight personal items as a result of transferring stuff from carry-ons to meet the 8kg weight limit - oddly, the solution was usually to carry a laptop sleeve or camera separately rather than pay to check something (I guess because the offending items couldn't really be checked in).
In Europe: Lufthansa, Swiss, LOT and KLM at irregular intervals, but my main airport is primarily small planes so that tracks. Though I've been pulled up in Munich and Zurich too. For the record, I've only ever had my personal item weighed or examined when my carry-on was large-ish and especially with wheels. (My preferred personal item bag is small enough that I've never actually been pinged - I'm just very short so an acceptable bag can e.g. look visually too big against my torso. Same with my carry-on).
Oh, and Easyjet at Gatwick, several times but not recently.