[Update April 3 '10: I see that a lot of people find this entry through Google -- Please leave a comment if it helped you! Plus, new discovery: Dishwasher detergent also removed old mold and stains from our white polymer shower stall (Corian-type material). Cover the stained area with a thick layer of paste and leave as long as you can. I treated a big pinkish stain for a whole day, then repeated to get areas I'd missed. Amazing how much less scary and low-rent our shower looks now.)
[Update March 4 '10: I was right; you don't need to use a whole bottle. Again, not the Dawn or Palmolive or whatever you use to hand-wash dishes in the sink, but the pastier, concentrated liquid detergent that goes into the dishwasher. Coat the stain with a thin layer of paste. Leave it there 5 minutes or longer, then rinse. If it ain't white, let me know about it!]
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Accidental discovery: Our kitchen has a white enamel (or “porcelain,” as I incorrectly call it for reasons unknown) sink, and despite our efforts with bleach to remove stains from tea, blueberries, etc., gradually the sink has been getting yellower and yellower. Especially around the drain. Ech.
Recently I dumped out some old dishwasher soap that I’d been informed had gotten too gloopy to use in the washer. Planning to recycle the bottles, I let the soap drain into the sink, where it made a layer about a half-inch thick. It sat there a couple hours while I did other tasks. When I came to rinse it out: White sinks! (It didn’t remove scorchmarks, but it clobbered everything else.)
I filled the sink with water, dumped in the remaining liquid and left it for a few hours, stirring occasionally. This whitened up the sides, too.
So try coating your white enamel sink with a layer of dishwasher detergent and letting it sit awhile. I’m sure you don’t have to use a whole bottle. But regular hand-washing dish soap has never done my sinks much good, and this does. No scrubbing, either!
my Aggie Journalists blog? It's over 
I'm not doing these right now because my life kind of went upside down, but thank you guys for the nice comments. I left all the stuff up 
You deserve a ton of credit! This IS the solution to getting your sink back from the dead! We used Palmolive Gel and followed your instructions.
Thank you!
Thank you thank you for leaving a note! That really brightens my day.
I’m so glad it worked for you. It also just worked on a Formica countertop, though that was a new stain which probably helped. Seriously, I’m so pleased to get your note, and glad for the report from the field, too!
OMG! I had tried everything! Thank you so much. I was just about to remove the sink and buy a stainless steel one. I loved having a white sink but it had become disgusting despite all my best efforts. Such a simple solution!
My husband said if bleach didnt work no way will this but it did!!
Thank you Sue!
This makes me happy – thank you for writing! I did think there must be bleach in the detergent, but yep, when we tried straight bleach we had no luck either. Maybe I’ll take a closer look at what’s in this stuff. Very glad your sink looks better and isn’t driving you nuts (I’m the same way). Yay!
Thank you, thank you, thank you. I will try it asap.