Can anyone tell me how long it takes to get from McGarran International Airport to the Las Vegas Strip?

Depends on where on the Strip you are going...it's a long drive from one end to the other. We were there in Nov. and took a shuttle, and with several stops to drop people off at various hotels, it took at least half an hour. Might also depend on what time of the day your are traveling. Traffic can get pretty heavy at times. Just glad we didn't have to drive in it.

Example:
from the aiport to Ballys was about 15-20 minutes.

When we arrived on a Sunday evening, we caught a cab to the Luxor, which is on the south end of the strip. It took about 10 min/$8). After freshening up, we took a cab to Treasure Island for a show, which is at the North end of the Strip - 2 miles one way. It again took about the same time/cost, even though traffic was brisk. When we left 8:00AM Thursday, it was SO EASY, it only took about 5 minutes! If you're pressed for time, take a cab - if you want to save the cash & have the time, take a shuttle.

Just for reference, the airport actually runs right next to the south strip. It's not even a block away.
But to get from the actual terminal curbs to one of the hotels takes about 5 minutes by car if you hit a couple red lights.
The north end can take 15-20 minutes, longer if traffic is really heavy.