I'm not a photo power user like you are by any means, but I've been using darktable[1] quite a bit lately and I've gotten to where I like it. Here's the blurb from their front page:
"darktable is an open source photography workflow application and RAW developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them."
Darktable isn't half as useful as Picasa for photo management, and the UI is awful. It does have some nice editing features, but it's a very different product.
"darktable is an open source photography workflow application and RAW developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them."
1. http://www.darktable.org/