definately get one but you'll have to remember these
(a) a pola filter usually reduces your exposure by three stops but if you have TTL (through the lens) metering this isnt an issue, if you don't have TTL metering you will have to compensate
( the most extreme colour change is not always the best, you have to use your eyes to find the best angle for the filter on a particular shot
© As you have a digital camera only use a circular polariser, don't use the t'other sort (linear)
(d) CP filters as well as being used for colour enhancement are also used for reducing (or enhancing) reflections in glass, water etc
(e) don't use a CP filter if you are shooting a panorama, the Filer will have a greater / lesser effect as you sweep round the image you are shooting
using it with the UV filter? well it depends if it makes a difference to the exposure (a UV filter reduces exposure by about 1/2 a stop), generally I keep the UV on the lens 90% of the time, sometimes though I take it off if it gives me that crucial bit of leeway in the exposure
The key to the CP filter is experimentation, its all about working out which angle on the filter gives you the best result at the time. It also has a greater / lesser effect dependant upon your position in relation to the sun
Other filters to consider? - a set of Neutral Density graduated filters to help balance exposures between the sky and the land in a photo
My advice would be to buy a filter system if you have more than one lens (or intend to upgrade to SLR) like the Hoya as every lens will require a different sized CP filter depending on its thread size, buy a system (Hoya etc) where the filters are held in a holder in front of the lens and you will only need one CP filter and given their price in the long run you will save money