How to figure out polarity of a polarized capacitor in a circuit
Capacitors having the same capacity are not all the same. If a designer uses a non polarized cap, e.g. polyester or ceramic, usually there is a reason for it. You cannot usually replace a 1&mu;F polyester cap with a 1&mu;F electrolytic one without consequences. There are many more factors involved in non-trivial circuits that mandate a different technology for caps. For example, electrolytic caps can have rather large ESR (equivalent series resistance), in other words they act as a cap with a resistor in series, and this could alter (for example) the bandwidth of an amplifier or the switching time of some driver circuit. Electrolytic caps are more prone to failure due to thermal stress: they don't like to live near heat sources and they may fail miserably if, let's say, they are put near another component that gets too hot (some electrolytic caps are rated for 80°C max, and some power circuits may get hotter than this in some places).

EDIT

To be clearer about that. Substituting a cap type with another should be done knowing at least some basics about the different technologies and their advantages and drawbacks. As a more evident example of this, consider that in some schematics you'll find two caps in parallel across a power rail and ground, one could be (say) 100&mu;F electrolytic and the other 100nF polyester. A 3 order of magnitude difference! Knowing only that two caps in parallel are equivalent to a single one having a capacity that is the sum of their capacity would lead to a puzzling question: "why the 100nF one is needed, since its capacity is swamped by the other one?". The answer is: the bigger one is there to store energy, helping leveling out voltage dips due to peaks in current demand from powered circuits, the polyester one is there because the ESR of the electrolytic prevents it to be a real short circuit for high frequencies, therefore high frequency components that may reach the rail are shorted to ground much better by the 100nF.