I think this has become a much bigger issue since the Q400s joined the fleet, and wonder what its like on the 763s with small bins?

The 737 bins are spacious, but the Q400s are unforgiving - every Q400 flight I've been on with encore has had at least one gate check recently. The bags are always these enormous ones that anyone could easily spot at the gate, but somehow, they get on. I don't think Westjet needs to be like AC and crack the whip, but eyeballing bags to spot the clearly oversized ones should be a regular occurrence. The bins can take a 22X16X10, so over Westjet's limits, but once you go bigger than that (esp. depth), you're in trouble, and these bags are usually easy to spot (fully expanded, bulging, clearly over-packed).

Personal items, I find, aren't the problem. People just tend to put them in the bins, which is a pain.