According to my stats at U2gigs. 52 times. Three of those shows were "short" shows. 2 Songs by the Dalton Bros on 11/18/1987, 3 Songs by full band at R&H Los Angeles Premiere (My footage is in "From The Sky Down" see avatar), and two songs by Bono only at Amnesty International 'Human Rights Now' show in 1988. So technically/officially, it's really 49 times.
Complete list here: http://www.u2gigs.com/myshows/22076