McCarran seems to have cleaned up its security-line act since the mid-00's. I can remember spending twenty minutes in line on a Sunday afternoon. I was there a little later this year, around 4 pm, and I breezed right through and was early enough that I would have made the earlier flight to MDW if it weren't full. Also, the cab line on a Friday night used to be a nightmare; this time, instead of waiting thirty minutes, we got a taxi right away.
This place has been a thorn in my side for a long time, though. One year they had a blackout. A blackout in an airport! Who ever heard of such a thing? Another time it rained and flooded the runways; about 90% of the flights were delayed or cancelled. I was forced to spend an extra night in Vegas (and not the fun way).
This year, one of the two trams was broken, so we had to wait a few minutes. My friends who arrived earlier in the day said that there were huge crowds waiting for the tram.
So under the best of circumstances, McCarran does what it's supposed to do. Otherwise, watch out!