Is there a size limit to an Adobe Lightroom catalog?

Is there a severe performance penalty for large catalogs, i.e., more than 50,000 images?

The upper limit I believe is around 500,000.
With any database of any kind (for images) there is always a performance hit the more images you have in it.

LR catalog management is something that I'm very passionate about.

Since a catalog is merely a pointer to the original images, I don't see the need to have one giant catalog with everything I've ever shot in it. My catalogs are organized by category. For example, I have a MacGroup catalog, a Landscapes catalog, a Family catalog, a Work catalog, etc. etc. My largest one has around 27,000 images in it (and technically that could be pruned way down if performance starts to become an issue).

I see no need to have say my MacGroup pictures and my Family Reunion pictures in the same catalog.

Catalogs can be imported into other catalogs. Images can be in multiple catalogs.

You can really take advantage of catalogs if you devise a system that works for you.

Stepping down off my soapbox now...

Thanks, Terry.

I'll probe the limits of my system with about 125,000 images and use LR to sort them into manageable categories.

This is not a short term project.

Does Lightroom work with DVD juke boxes for large collections of images?

Lightroom will work with any mountable volume. So if the Finder can see it, LR can see it and catalog it.