For me, Aperture is faster for sorting and selecting on my G5 PowerMac ( single 1.8 ) with a FX5200 (which is lower than min spec) than Lightroom. The way Lightroom generates thumbnails after import drives me nuts (however, I havent downloaded Beta2 of Lightroom yet). The loupe and workflow in Aperture is very nice and very keyboard-able.
On a decent highend graphics card Aperture must fly and I cant wait to see the intel version running on the new iMac; that might give me an excuse to splurge
Aperture has a lot of promise, but IMHO its not there yet in a few regards. The raw conversion isnt stunning for the D70, my main grizzle is noise and Aperture does no NR by default. Coupled to that the NR tools seem quite limited and coarse, not to mention that once you start doing any major
mods to the pic, my under-spec graphics card turns Aperture into a bowl of molasses.
Basically, unless you have a Mac with a HIGH-END graphics card (think X800 or similar) then I think you might be frustrated with Aperture compared to Lightroom if you are doing much more than using it for sorts and selects (which I do as its great for this). This app is NOT hugely hard on the processor, it is VERY graphics-card intensive. Apple have written it in a way where it does most of the work on the graphics card processor/memory, not the main processor/memory. So a good fast graphics card with plenty of memory is a necessity, not a nice-ity.
There are a few other things that Apple need to work on as well, such as using other RAW converters without jumping through hoops. Its also not quite there as a DAM either, hopefully they will give some thought to this in the future. Something that I was suprised about is the lack of an ability where you can archive photos to offline storage (or another disk) and still have the ability to view thumbnails and search on metadata (similar to iView). There are ways around this and I really like the 'Vaults' idea for backups, but to me this is a glaring ommision.
Please note. Aperture does NOT use a 'non-standard single database' to store photos!!!
It stores its files in a folder structure that is merely a standard package. If you right-click on the package, you can browse down into it and Spotlight finds the files in there fine. Building smartfolders is the easiest way to access those files. I notice iPhoto6 has the ability to use photos outside its own import reigeme so I think its likely this will be coming in Aperture as well.
Go and have a read through the Aperture forums on apple.com. There are a lot of people on there using it very successfully (commercially) where its current feature-set suits their workflow and requirements. You will also find a lot of noise on there from people who feel short-changed and feel that the reality didnt meet the promise.
I do believe that Aperture (a version or so down the road) will actually end up being the bees-knees, especially once the consumer level hardware catches up with the s/w (maybe already has with the intel iMac??). After spending a reasonable amount of time trialling it, given my current hardware (graphics card), I wouldnt buy the current version. However, I expect that version 2 (or 3?) will fantastic enough to warrant me upgrading my hardware so I can buy the s/w.