I recently switched to LR3 (Provided nothing disastrous happens before the 30 day trial is up).
Pros of Aperture 3:
-Great UI
-Some more "fun" features, like faces and all that
-Fast and Easy to upload images
-Love the plugin interfaces and functionality
Cons of Aperture 3
-In my experience doing pro work with large images, it would crash / need force closed a couple times an hour, no joke.
-Took FOREVER exporting images, even web-sized watermarked
Pros of Lightroom 3:
-Quick. Very quick.
-Great Noise reduction, great processing in general
-LENS PROFILES! This was what pushed me over the edge, aside from the incessant crashing of A3. I have already saved hours after only one wedding by using automatic profiles to correct distortion on my UWA shots.
-Water mark and export options are 10x better for my needs.
Cons of Lightroom 3:
-UI is disastrous. Still fumbling around a week later.
-UI is THAT disastrous.
-UI
-UI
