As title, has anyone done this?
How do i mix it?
What should i expect to happen?
How long does it take?
Will i die if i get it wrong, or worse will i ruin my steel frame?

most of what you need here or on sheldon brown.

[video]http://www.youtube.com/watch?v=-dYnSVVDxrE[/video]

I have done it.

Mix up caustic soda with water as described on the bottle to the strongest mix (mine said for paint stripping).

Pour caustic soda into frame through bottle cage bolts on seat tube with frame upside down using a small piece of aquarium hose and a small funnel.

Leave for 3 days I did try each day. After 3 days you could just see that liquid was seeping down the seat post.

Remove saddle and put end of seat post in a vice and twist.

No damage to frame, seat post is obviously no use afterwards.

Make sure you collect and clean off any spilt caustic soda it killed a big patch of my lawn even though I washed it off almost instantly with lots of water.

Is it carbon or ally? My carbon post was properly seized into my steel 456. I liberally sprayed it with WD40 and let it sit overnight, repeated it, then applied heat from a heat gun to the frame (not enough to damage the paint but it was fairly hot to the touch) after which it slowly started to move and finally came out.
Caustic soda is fairly nasty stuff. One thing I do know is that you add the powder to the water NOT the other way round.

Be *very* careful with caustic soda and follow the instructions.

Nasty stuff so treat with care.

Be really careful with Caustic.

Wear gloves if your hands feel slippy/soapy you need to wash in plenty of water or a water/vinegar mix. Failure to do this could lead to a bit of degloving.

I wasn’t the one who carried it out but I can confirm it worked on my old fixie when all else had failed.

Alloy post, steel frame.