Make sure you understand the difference between cleaning, and then sanitising.
Cleaning is removing soil buildup and beerstone. In kegs, especially in commercial breweries and pubs sodium hydroxide is used. This stuff is extremely corrosive. Please read and follow every safety direction you can find. I do not use this stuff often, and cannot remember the correct amount to use.
Other detergents may or may not be suitable for stainless steel.
Sanitising is killing all the bugs on a cleaned surface. Many cleaning agents do a good job at this, but must be rinsed thoroughly as they are not wanted in a glass of beer or in your stomach. After rinsing, the lines and kegs are at the same sanitation level as your rinse water, be it good or bad. Most brewers use a no rinse sanitiser such as weak phosphoric or iodine after a thorough cleaning and rinse out of the detergent.
Sodium percarbonate is an excellent cleaner for stainless steel, plastic and glass. This information came from a metalurgist and reading. My kegs often get a soak for days at a time with 1/4-1/2 a cup of homebrand napisan which is sodium percarbonate and topped up with water. Very occaisionally, they get a sodium hydroxide soak if there is a beerstone buildup from previous owners.
Redbeard is confusing bleach and sodium percarbonate. Bleach is corrosive to stainless steel, do not use it.
I am under the impression that the use of sodium metabisulphate is bad on stainless steel, but cannot remember where I read this, and have not come across anything to back this up. The issue of sodium met as being unsuitable generally in breweries has already been discussed in a previous thread. There are far better products to use.
For further reading, check out earlier threads, the brewwikki site and John Palmer's book.