Custom U.S. - Polish Keyboard (for OS X)
For typing Polish on OS X, I created my own simple custom Keyboard based off the standard US keyboard. A full discussion can be found here https://github.com/defuncart/custom-osx-us-polish-keyboard, but in brief, it uses the ⌥ key and various states to type the various accented and special characters.
Thus, ⌥l = ł while ⌥e + n = ń etc.
If you have used the US keyboard to type any accent or special characters before, then these type of key combinations should seem familiar.
Installing and learning the real polish keyboard may be more suited for some, but at least in my case, this custom keyboard allows me to easily type in English, Irish, German or Polish without cycling between installed keyboards or learning new kid bindings.
Perhaps it may also be of use to others. There aren't any install instructions as such as it is assumed that anyone who wishes to mess about with such stuff actually know what they are doing :)