I have three 67mm filters - a CPL, an ND grad, and a NC/UV filter - and a step up ring so I can use them on my 52mm lenses. The only time I've ever used the UV filter (and the sole reason I bought it) was taking photos on the flight deck of an aircraft carrier where you have steam, jet exhaust, sea spray, grease, pieces of non-skid getting blown through the air, etc.
The filter I've used the most is the CPL. The grad filter has been useful, I just haven't encountered scenes that would benefit from it as often as the CPL. You'll see two main points of view on the UV filters: people like your friend who won't leave the house without a UV filter on the lens to protect it, and people who don't feel the risk of glare, reduced contrast, etc. from putting another piece of glass in front of their lens is worth the protection that a filter would give. Read through that link from ByThom, he's very clear on his point of view.
The filter I've used the most is the CPL. The grad filter has been useful, I just haven't encountered scenes that would benefit from it as often as the CPL. You'll see two main points of view on the UV filters: people like your friend who won't leave the house without a UV filter on the lens to protect it, and people who don't feel the risk of glare, reduced contrast, etc. from putting another piece of glass in front of their lens is worth the protection that a filter would give. Read through that link from ByThom, he's very clear on his point of view.
