Ninja originally used `.d` files as well (it was built while incrementally replacing a make-based system so it did many things like make). My recollection is that it was already faster than make without the deps log, but it is almost certainly project specific, and perhaps due to the ways we were abusing make (search for "clever hacks" on http://neugierig.org/software/chromium/notes/2011/02/ninja.h... for some discussion of this.

With that said, the deps log processing of .d files was a huge win for us. One thing to observe is that it's the same code and amount of work either way, but if you load them at startup they are processed during the critical path, while the deps log parsing happens during the build so their cost is amortized.