Painting: Sand down to the metal?

Ok.. Give me your opinions. I'm thinking of painting the case (I painted one in the past without sanding down to the metal) but should I? What are the pros and cons of spraying on metal in oppose to smoothing and spraying.

Also, what grit of wet/dry is the best for this particular task?

no not all the way to the metal...

check this guide out: here

Check out the sticky at the top of the page.

When I painted mine I sanded all the way down to the metal just cos I'm a bit of a perfectionist and like to try and be thorough. I don't think it's really worth it though - took me a few days, working 2-3 hrs a day at it with a piece of sandpaper and elbow grease! If I was doing it again, I'd just sand the original paint nice and smooth - I think I actually got it smoother while sanding the paint than it was when I'd got it down to bare metal.