I shoot both (two card slots), sending the raw files to slot one and the jpegs to slot two.
Nine times out of ten I work on the raw files. I rarely get it right straight out of camera.
So I go through all the jpegs really quickly and take a note of which ones I want to work on (over in raw, of course), and the few that come out just right I slip into a "finished" folder for that project.
Then, once I know which files I like, I go to Lightroom and work on those raw files, import them to another folder as TIFF files, work on them with Photoshop (if necessary) and then put them in the finished folder. I also frequently can go from raw straight to jpeg in Lightroom if I don't have to do much to it.
Sometimes while going through Jpegs I'll open one up in Photoshop, work on it a touch, and then save it to the finished folder. This isn't really a good idea, but I do it anyway.
The point is that you shouldn't open jpegs to work on them, because a Jpeg is a finished photo. When you open it and then save it, you compress info that was already compressed in the first place. If you constantly open, adjust, save, open, adjust, save a jpeg, it's like pouring water from hand to hand. Eventually you'll have nothing.
You should always shoot in raw, and if you are kicking but or in a hurry, shoot raw + jpeg. But Jpeg is for finished photos.
Let me say this: I am deeply in love with Lightroom. It can do miracles with raw files.