its quite a harsh process apparently. the stuff they use contains lots of chemicals including those found in perm lotion, and its very drying and damaging to your hair.
are you wanting to go from dark to blonde?? if so, see your hairdresser id say... it can be done at home with a pre-lightner then normal hair dye. but... to be on the safe side, hairdressers would be best.
another thing to try if youve dyed your hair and think its too dark, is vosene shampoo. it stinks, but it lightens hair.
Apparently Pantene strips your hair colour according to my hairdresser as does Head and Shoulders, you could try using that until your hair lightens to a shade you like.
I've had mine 'stripped'' twice and the first time was a disaster as they managed to lift a fair part of my scalp as well. The second time when I wanted to go from shocking pink to blonde I had it done at a very reputable salon who rang up the manufacturers for advice before proceeding, and my hair was fine afterwards...