I've tried and liked it, but it seems that it isn't really meant to replicate Lightroom's cataloguing functionality. I tried importing the 20 or 25K photos I have, which Lightroom cruises through (I've met people with hundreds of thousands of photos in their catalogues) and Darktable gacks. That's on a relatively recent 5K iMac too, so I don't think hardware limitations are the problem.

Right now Darktable seems to be more of an editing tool and less of a cataloguing tool.