I've never actually used Bibble. I have roughly one year of my shooting in "converted" DNG format (having discarded the original raw files). Since Bibble doesn't support this, that was a deal-breaker for me. Perhaps I should revisit Bibble.

As such, I can't really offer a meaningful comparison between them. What's eminently clear is that Bibble's authors are performance nutcases, so Bibble should run significantly faster than Lightroom. If you're on older hardware, that's a big consideration. On the flip side, Lightroom's UI is supposed to be better and there's real third-party plug-in support now. (For example, I regularly use the PicasaWeb exporter from Jeff Friedl.)