The Salt Lake area does have more rail when counting Frontrunner. But if you compare just Light Rail track mileage, we are nearly even currently.
http://en.wikipedia.org/wiki/List_of_United_States_light_rail_systems_by_ridership
This shows that we are ahead of the Denver area by .3 miles or .8 kilometers.
I know that built environment plays into usage a bit but to think that Denver with roughly the same light rail track mileage, has only just over 4,000 daily riders more than we do.
Now, the Denver area does have more light rail coming online in the next 10 years than the Salt Lake area. So the gap between riders may tip only to Salt Lake for the short term.
Someone correct me if I am wrong but I think that once Denver has all of their light rail built, they are projecting to be near 100K riders daily. I don't know if this number is strictly light rail or if it also includes commuter rail as well.
I think that the 2015 projections for UTA rail ridership (Trax and Frontrunner) is close to 80K daily riders.
One thing I do like on the Wiki list is that we are more than 8,000 riders ahead of St. Louis yet, they have more than 10 Miles of extra track.
I do hope that no one takes this as a city/city competition. I was just trying to show that the Salt Lake area does on average better light rail ridership than larger cities with equal or near equal amounts of light rail track.