hmm no idea, i was afraid of this too when i moved into my condo with original 1950's cabinets. My best guess tho, is they probably hold more than the cheap new particle board ones do. I have my loaded up and they haven't budged. You could always weigh them and test load them with something else...

This info is available from the manufacturer, so I would find a similar cabinet and look it up. That being said, load capacity for a low-end wall cabinet is usually 30-50 pounds.

Most older homes built more than 30-35 years ago generally don't have modular cabinets like newer construction has today, and thus may well be built on site in many cases.

That said, I'm sure those older cabinets are mostly solid wood, and thus should hold up to heavy stuff in them. I have older cabinets myself and they seem to hold up just fine, despite being over 50 years old.

You can find this out with the method described by Calvin's father:
http://www.s-anand.net/blog/calvin-and-hobbes-dad-explains-science/

Is that a picture of your cabinet?

If you have solid wood shelves (as they often were back then) I wouldn't worry too much about it, but maybe take care to spread out the load evenly per shelf and maybe delegate an extra shelf to dishes so they're not all on one. If you're really concerned or start to notice bowing then reinforce the shelves against the back/sides/center upright with L-brackets, they are cheap insurance.

We're the proud owners of tipping cabinets, so I can tell you one problem would be if the wood got warped from humidity, as ours did. Eventually the cabinets began to sag. Keep an eye out for any changes in the shelf level.

Thanks! I've been just keeping an eye on them, and so far so good. I imagine in their 6 decades on the wall they've seen a lot of dishes, so ours are probably nothing too stressful. I guess we'll find out!

And no, that's not my cabinet--mine are your standard honey pine. We plan to paint this spring, as their color hasn't worn evenly over time, particularly in heavy-use spots, and the hardware (those long straps that cover half the door width) aren't for us.

Dragonmama, a most excellent answer.

As for the shelves, with the glaring exception of Corelle, most dishes were heavy. Think Fiestaware and good china. Maybe if you have settings for 16 of modern day 14 inch plates from restaurants, yeah, worry. Aside from that? Test!