I've been working on the append-only storage engine for jSuneido and most recently dumping and loading. I was flipping back and forth between storage engines and it seemed like the new one was faster. I decided to time it and sure enough, with the new append-only storage engine, loading a database was close to twice as fast - nice!
Note: This was not any kind of scientific benchmark. It was a relatively small database (130mb) and only loading. But still, a promising early result.
This is also still single-threaded. I've been itching to try using multiple threads to build indexes. Each index is relatively independent so it should be feasible, but I'm currently using an "exclusive" transaction so it's a little tricky. This should speed up loading even more.