I was in the Heritage Drive Costco on May 29. While there was a short wait (7 minutes) in the line outside, there were definitely more customers in the store than in previous weeks. Not crowded, but busier.
As for waiting in a lineup to get inside the store? I think this temporary exercise in social distancing should become permanent. The longest I stood in a line at Costco was 34 minutes; started the maze 3 switchbacks out. But the total time to shop was much less than normal due to fewer people to get in the way, almost no shopping cart traffic jams, and shorter checkout lines.