The Toughest part as everyone has said, is getting the pulley nut(s) off. And without trashing anything in/on/around the engine. Take my word for it, i know from bitter experience that you definitely want to use an impact wrench and not to try removing this big, tight bolt with 4 foot long breaker bars, etc.
Also you definitely need an impact if you are 1)changing CV drive axles, 2) removing a flywheel for some reason 3) nice to have when changing wheels for rotation. But who wants to spend $300 for an air compressor and another 50 or 100 for animpact wrench.
After years and years of trying all the hard ways i got an electric impact wrench, $300 from Sears. ( Its not as powerful as an air impact but it just pounds off the bolt, you just keep at it and it beats the bolt loose. Havent found anything it couldnt break loose yet.) Now the price on this same impact gun has come way down. But since you are probably using it only a couple times in you life syou could go with a cheapo model, as the saving on labor of having work done pays for it easily.
http://da.harborfreight.com/cpisearch/web/search.do