The speed argument is over. Perhaps, though, I should say that it has just begun. Nobody argued that Aperture 1.5 struggled for performance whilst Lightroom does not. Aperture 2 certainly now appears to bear serious comparison with Lightroom 1.3 on performance.
Aperture 2 has a "Quick Preview Mode". Basically, this appears to turn off the rendering of adjustments on top of the RAW file and instead just displays the JPEG preview. Adjustments are disabled in this mode but I can give you three words on this: Faster. Than. Lightroom. Quick Preview might well also be called "Laptop Mode". It is an insanely fast way to do an initial one-to-two-star editing pass.
I shot a number of images today with my 30D's picture style set to Monochrome. My understanding of this, when shooting RAW, is that it doesn't discard RAW colour information, but it makes the embedded JPEG preview monochrome. When Aperture is in Quick Preview mode, and it hasn't rendered its own previews, it uses the embedded preview in the RAW file. The images I shot using the Monochrome picture style were rendered monochrome in Aperture, even though the RAW data had colour information.
Lens Model metadata is finally here. Hopefully I can modify FlickrExport to automatically pick that up as a Flickr tag.
Many of the adjustments feel much faster. In particular, the Straighten adjustment has always been very slow on my machines. Now it's like greased lightning. Lots of the new adjustments look good too, but I haven't been into them deeply yet.
Aperture 2 supports background exporting, which means that there's no longer any visual feedback on the operation. This also applies to export plugins like FlickrExport. I'm not 100% sure I like this but I'll get into it more as we go and see what's really going on.
There's an image adjustment API in Aperture 2. If someone can persuade Imagenomics to port Noiseware Pro to Aperture, I will be a very, very happy man.
Overall, it seems like a very nice upgrade. I'll be interested to see how it likes my master library of 30,000+ images, but it's infinitely more usable on my MacBook Pro than Aperture 1.5 was.