I have some 330 uf and 220 uf caps i want to use as decoupling caps. One of the legs on the cap is longer than the other.
Does this mean that one leg is positive and the other negative? Or does it not matter?
Indeed, it does matter. Devices with the capacity you have are almost completely certainly electrolytic (notice the wiggle words, I haven't seen everything...yet). If there is a stripe on the side of a can type cap, that usually is aligned with the negative terminal. The positive terminal will also (usually) be longer. The negative terminal is also (usually) connected electrically to the outside of the capacitor "can", if it is a can type.
For surface mount devices, all bets are off, although MOST tantalum surface mount devices have a stripe at the POSITIVE end, just to confuse the issue.
I use a large quantity of surface mount LEDs, in three different colors, but the same package (0603). Red and yellow are marked ->+ (bass ackwards), while the green is +>- (normal). When I pointed this out to the manufacturer(s), they said pay attention to the data sheet.
Pay attention to the data sheet. Pay close attention to the data sheet.