The really big difference between AP and LR is the mental model. The rest is detail. LR is modular, AP isn't. With LR you adjust images in Develop (or Quick Develop). With AP, you adjust them anywhere. Takes a while to get your head around this (well, it took me a while), but once the lights go on, they stay on. AP is far more revolutionary and imaginative than LR, but that isn't necessarily a good thing in itself.
Whilst I think that AP is a better DAM at present (actually much better), I think the real question is do you work in a linear way or not ? If you're linear, methodical, then LR will suit you. If you're more random, or impulsive (or have attention span deficiencies) then AP's your think. Of course, if you use a PC then you have no choice (strange as that sounds).
There is of course the small matter than LR currently has far a more flexible and arguably better RAW engine - but then again I can think of at least two RAW engines that I prefer to Adobe's. And AP is better at working with external applications - including Photoshop.
As for performance, well I find I can run AP on a 2Ghz MacBook (not Pro) quite adequately. And AP is perfectly happy to import 200Mb .PSDs and TIFs originating from film scans.
Honestly I'm still using an iView based workflow, and I'm not going to switch until I've had a chance to see how Microsoft's ownership of it changes things. But if I had to choose now, I'd choose Aperture.
Finally, if LR is so intuitive, why do we need so many bloody books, DVDs, Broadway Shows and Cruise Tours all about using it ?