Well I just pre-ordered Adobe Lightroom (LR) a couple hours ago. About a week or two ago I started using the LR beta to manage my digital photo workflow--basically going from importing, to rating, labelling, adjusting, and archiving. The initial reason behind my adoption of LR over iPhoto was that LR allowed me to manage the organization of the photos on disk. But through using it I found it much easier to actually "process" my photos and also be able to find them afterwards.
I will leave the in-depth details behind the switch once I have the 1.0 release (should be mid-February).