Stainless steel can have surprising failure modes. For instance, crevice corrosion[1].

The shiny stainless steel fittings holding up your sailboat mast can corrode straight through without more than some tiny telltale signs.

You can see an example here: http://forums.sbo.sailboatowners.com/showthread.php?t=107622 The manufacturing likely provided a tiny crack, splash a little salt water and next thing you know your sailboat's mast is in the water next to it trying to bash a hole in the hull.

[1] http://en.wikipedia.org/wiki/Crevice_corrosion

I work (partly) with the marine industry, where stainless is a common metal. The main problem is that there are many alloys of iron, of which that is only one, and each has its various benefits. Most bolts are rated grade 1-8. If a grade specific bolt is specified, then stainless is a problem. Or if vanadium (spring) steel is needed. Etc., etc.