When I started working with Raw in November, I really, really, really wanted to use Aperture. I liked iPhoto and Mac apps in general very much, so I tried to make Ap work, but in the end I chose LR. Local brush was a big reason. Also, I have a PC laptop from work, and I am able to put LR on there. And although the modules can somewhat get in the way, I like the LR interface better. I found the font size on Ap too small. Also, in LR I like the ability to make custom Presets.
I miss, though, soft proofing in Ap, and some of the DAM features in Ap and also the vault. So, I don't think it's a clear cut where one is better than the other. It depends on what you want and how you work.
Final reason for LR is photography (and images in general) is a big part of Adobe's business. Less so with Apple, so going forward I have a bit more comfort thinking LR will be here and progress, whereas Apple is know for dropping businesses they feel are not core for them anymore.
My workflow is just like Hector's above with a few minor tweaks:
Hector wrote:
1 - Import RAW album from camera to my own file structure on hdd (folders for year, month, album title) (I add "YYYYMMDD-" to the beginning of each file)
2 - Import (without moving) into LR library
3 - Post process everything in there, exposure, b/w conversions etc
4 - (Very rarely) further PP in PS Elements
5 - Export completed album from LR as jpeg to file on desktop (I actually put them in a folder "iphoto load")
6 - Import jpeg album to iPhoto for viewing (never editing) (I do make a copy of the jpg in iPhoto if I want different crops for printing)
7 - Upload from desktop to web (flickr, FB, .mac, Picasa, but I'm thinking about going smugmug)
8 - Delete desktop file (I delete the jpg desktop file, and then archive the raw files offline through LR).