A couple of examples plucked from Flickr should give you the idea:
Browse Flicker with "horizon202" as a tag for plenty more:
Pretty much anything rectilinear is going to curl in some way, whether the camera is level or not.
I picked up one of the sale-priced Perfekts too, to replace my broken Horizon 202. So I'll shortly be back to tinkering with swing-lens effects myself. Have fun!