The XPS is impressively quiet. The only time I ever actually hear it is if I'm using it in bed late at night. Otherwise the ambient room noise is much louder.
As far as size goes, it's a tradeoff. If the XPS had just average performance, its size wouldn't be justified. But since the XPS is so incredibly fast, I think it definitely is. I love the fact that I can take it to a lan party and outperform 90% of the desktop user. I like that I can do photoshop work without feeling like I'm on a laptop. Needless to say, I love mine.