From what I've been reading in the papers, those who do get
nabbed for watching and downloading porn were mostly those who were
already being nabbed for other crimes.
For example, let's say there's this fraudster who cheats old people
of their savings. He gets arrested in his home. When investigators
look through his computer files, they may encounter some downloaded
porn pics. So the fraudster will get charge with both fraud AND the
totally unrelated charge of possessing porn.
It's quite rare that someone gets charged for owning porn per se -
unless if someone else decides to saboh him, of course.