I've only had jeans hemmed a few times and never felt like I needed the original hem since I tend to wear non-distressed dark wash jeans. I did recently get a pair of James jeans hemmed at my local drycleaner and they had very slight fraying and a worn look on the original hems so I just buffed at them a bit with a piece of sandpaper so they don't look brand new and obviously hemmed. The tailor that I go to with important jobs is Madame Paulette's on 2nd Ave around 65th St. They are recommended in lots of magazines and do a great job. I'm not sure how much they charge for jeans though. I got a silk dress taken in last summer and it was $60, obviously pants would be much less.