No doubt most Mac users have been trying out Aperture 3.0. On Twitter and some forums, there has been the occasional users who have upgraded to version 3 reporting slower performance to what they expected. The majority of what I've read though is reporting faster performance, which is something I totally agree with.
I have two tips to help out those who may be experiencing slow systems; before that though, you should ideally upgrade to 4Gb of RAM. Being a 64-bit program it can manage extra RAM extremely well, so the more loaded your system, the more obvious speed gains you will see.
Tip 1: In Preferences go to the Previews tab and only tick "Use embedded jpeg from camera when possible" and if you don't need it, choose to 'Never' share previews with iLife and iWork.
Tip 2: Aperture 3.0 now has the Faces feature. It has to be seen to be believed; it still amazes me how it can pick out faces throughout my Library and start to recognise people after they have been tagged a few times. Whilst this feature will be of great use to some, you need to realise that it's a very computer intensive process the first time it runs after an upgrade, or if you are using a trial and have imported many thousands of images. My suggestion would be to switch off the feature when you're using the program and then switch it on to run over night. Once it has catalogued the many thousands of faces, you won't notice a performance hit.
During my beta testing period, I used a 15" MacBook Pro with 2.53GHz Intel Core 2 Duo and 4Gb of RAM. It's definitely not the fastest in Apple's line-up but by following the above suggestions, runs extremely fast with Aperture 3.0.
Lastly, check out Mac Create for some great information on Aperture 3.0.