Depends on the Pentax in my experience.
There are a lot of broken ME Supers out there, but I'd suggest that this has something to do with the number sold (as compared to, say, the MX) rather than inherent unreliability.
I avoid the MZ series (ZX series in the USA) as that stupid plastic drive cog has a habit of splitting and rendering them useless. The Z or PZ series bodies seem to be more reliable but need a specialist battery. That's why my favoured AF body is an SFXn with the AA battery grip.
MEs, MXs and earlier seem to be almost impossible to kill, without resorting to serious maltreatment such as dropping from a great height. In fact two of my three MEs came to me as "spares or repair" lots. One needed a quick squirt of lighter fluid and a prod with a screwdriver to unjam it, the other just needed its battery cover cleaning. Both now work perfectly.