I strongly agree with the "don't do it" suggestions.
Some people have a need for totally isolated collections of images, such as business/personal, or to separate different clients' work. Otherwise I would not recommend multiple catalogues on one machine. LR doesn't cope well with the idea that images are in multiple catalogues, and moving things between catalogues is tedious and (IMHO) error-prone. LR works fine with catalogues of hundreds of thousands of images without slowing down significantly, and you have the advantage of searching/sorting over all your images.
So far as I can tell, the only disadvantage is that backing up the catalogue takes longer. My catalogue (for 64,000 images) is 1.3G, but what's a couple of minutes to back it up over a 100M network?