If you need something to vomit in on the way home from the bar, C-U taxi might fit the bill. But never use them for an early morning pickup to the airport. I've tried a few times in the four years that I've lived in CU with usually miserable results.
1. don't call the night before. they'll only lose your request.
2. don't believe them when they say "we'll be there in 5 minutes" This morning I waited for 20 minutes after I called to remind them that I needed a cab. Eventually had to wake someone to drive me to the airport. For all I know they never showed (I never got a call back saying they were waiting on me either.)
Friends say that Yellow Cab is better at this. (I saw two Yellow Cabs at Willard when I arrived).
C-U Cab (aka Illini Taxi) isn't getting any more of my business.