I have used stored energy in the form of weight but never compressed air... I had a 55 gallon drum filled with concrete that I could raise up with a chain hoist and then let it loose, on it's way down it powered a shaft for use with various tools in the shop. A very simple but very effective stored energy system.
I have taken quite an interest in stone as a building material here in the last few years and keep thinking of how much energy one could get from mining stone at an elevation and then dropping it like the 55 gallon drum from the elevation and using the energy to power things on the trip down.
I would imagine that air can be used in much the same way, just keep in mind the 20% loss of energy each time you transform from one form of energy to another such as air pressure to mechanical, mechanical to electrical, electrical to electric motor or electrical to battery etc... It doesn't take too many times before you have little left of the initial energy you tried to store left for use.
Like Einstein stated... "simplicity is genius", the simpler the system the better the efficiency and the more viable it is likely to be for you.
There is a research article cited in the linked article that mentions efficiency comparable to lead-acid batteries.
According to the article, the common way to do compressed air storage involves either large tanks at low pressure or small tanks at high pressure with inefficiencies in both cases. At low pressure, the tanks have to be enormous, but the electrical to electrical conversion efficiency is high. At high pressure, the tanks are small, but the heat loss during compression cause big energy loss that makes the electrical to electrical efficiency to be quite low (I think about 10-20%). The modular system has many small tanks at low pressure with some computer controlled valves. The smaller tanks help to alleviate the inefficiency due to pressure loss during emptying.
Here is a wind turbine for compressing air.
webpage These could fill a large converted propane tank. You can get kitchen appliances and many other tools to run on compressed air. This is popular in some amish communities.
I could see developing a compressed air assisted bicycle (that brought me here). Here is an explanation of different types of air motors for anyone looking to make a new tool or toy.
"We will never be truly healthy, satisfied, or fulfilled if we live apart and alienated from the environment from which we evolved." -Stephen Kellert