Happened to me
When upgrading my ~28,000 photo library to version 3, Aperture ballooned up to using all 3.5 GB of available RAM, then proceeded to leak into ever bit of free space on my hard drive for VRAM. It was approximately 2,000 photos away from finishing when the OS presented me with no choice but forcing it to quit.
So now I'm in a situation where I no longer have Aperture 2 installed, forcing me to use the partially-converted library temporarily to complete a project. Whenever 3.0.1 (or whatever) is finished I'll have to figure out a way to move those new photos to a temporary location, delete the new library and re-import the old one.
When upgrading my ~28,000 photo library to version 3, Aperture ballooned up to using all 3.5 GB of available RAM, then proceeded to leak into ever bit of free space on my hard drive for VRAM. It was approximately 2,000 photos away from finishing when the OS presented me with no choice but forcing it to quit.
So now I'm in a situation where I no longer have Aperture 2 installed, forcing me to use the partially-converted library temporarily to complete a project. Whenever 3.0.1 (or whatever) is finished I'll have to figure out a way to move those new photos to a temporary location, delete the new library and re-import the old one.