I might have got it wrong, but in the spanish edition of Scott Kelby´s "Adobe Photoshop Lightroom 3" on the page 108, under "creation and use of various catalogs" it goes:
"LR has been designed to administrate a library of, literally, tnths of thousands of images and I know about photographers that have 50.000 or 60.000 images in their catalogs and, even though, LR is able to work with them. Anyway, once your catalog is getting so big, LR will start to work slower. Thankfully tou can create more catalogs ..."
The translation is as close to the spanish version I have as I´m able to produce.
I read this same thing in other places, probably deriving from this same sentence?
Thanks a lot for your advise, I feel much more confident now with bigger catalogs, wich suites me much better in my workflow.