I use a lot of stainless and have for some years now. The advantage is if you have a lathe you can make all your own nuts and bolts, screw etc and they dont have to be plated. You can buy hex bar in the correct BS sizes.
There are quite a few grades of stainless but as a general rule you are only likely to come across two of them, 304 and 316. 304 is the most commonly used one for nuts and bolts, if you go into a shop and ask for a stainless bolt most likely it will be 304. 316 is quite often refered to as "marine grade". 316 has molybdenum added to it to increase its resistance to corrosion in harsh environments ie. the ocean or extreme weather conditions. The molybdenum also makes it much harder and gives it a higher tensile strength, its very hard to strip a bolt made of 316. The downside is its hard to work with and blunts taps and dies etc very quickly.
Another problem with stainless is galling, or "picking up" of the threads. Sometimes if you screw a nut onto a bolt you simply can not get it off again.
As I said I use it a lot, most of my bikes are entirely held together with stainless bolts. I have made axles and just about everything out of it and have not had a failure yet. I use 316 even though it is harder to work with, it is strong and does not rust.