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Regarding keywords and the organization of your images in Lightroom, have a look at this thread. BTW, ever since upgrading my machine to 8 GB RAM, I haven't noticed any slowdowns in Aperture -- even in larger projects.
 
I have used aperture on an imac with 4gb ram and the only time it wasn't enough when it upgraded the aperture 2 library to 3 and it has at quite a lot of pictures
 
You need to think very carefully before switching digital asset management platforms.

Both A3 and LR3 are full fledged RAW editors (LR3 maybe even more so, as more of Photoshop's features are integrated into it) as well as photo databases. The changes you make to your photos in one platform won't be picked up in the other. If you're just starting, that's not really a big deal. If you have a huge catalog of photos... you can imagine.

Honestly, I'd rather switch camera systems than switch DAM software.
 
You need to think very carefully before switching digital asset management platforms.

Both A3 and LR3 are full fledged RAW editors (LR3 maybe even more so, as more of Photoshop's features are integrated into it) as well as photo databases. The changes you make to your photos in one platform won't be picked up in the other. If you're just starting, that's not really a big deal. If you have a huge catalog of photos... you can imagine.

Honestly, I'd rather switch camera systems than switch DAM software.

Agreed, I tried and failed. I went back to Aperture 3 after trying LR 3 and I have to say , once I got into how Aperture 3 manages projects, folders files and referenced files it flies and its EXTREMELY intuitive...
 
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