This effect finds its way into what I do probably more than almost anything else I own. :) Excellent for when you don't want a "cyclic/rotating" chorusing effect, but just want to sound bigger and "wider", on synths/keyboards, vocals, guitars, etc.
Great on guitars when used subtly (especially when used in conjunction with mda's excellent Dynamics compressor), especially when going for a clean, ring-y 80's-style Strat sound ala' Robbie Blunt (Robert Plant), Jamie West-Oram (The Fixx), Alex Lifeson (Rush), etc.
On pianos, can provide a sound similar to the old Yamaha CP-70/80 series electric grand pianos from the 70's/80's....or out-of-tune honky-tonk pianos with more extreme settings, for those times you wanna play ELP's "Benny The Bouncer." ;)
On vocals, great for disturbing evil-sounding doubled vocal effects when used with extreme settings.