Read this news about ubuntu going to out-pretty Mac in 2 years. I'm not disputing the possibility but I have serious doubts if this is going to materialize. Art is really personal and I don't think "design by committee" really works.
Linux wasn't too attractive at the start to me, I had a book that I never read. I tried ubuntu last year its outlook wasn't attractive either. I would say it is pretty ugly comparing to what you can get from a Mac. Obviously developers have devoted a lot of time in catching up or surpassing Windows on usability and functionality. It's not wrong and look and feel is a matter of taste. I have tried a dozen distros and every time I reinstalled my copy of ubuntu tweaking the font is the first thing I do.
Just more than a year ago when Apple first release beta Safari for Windows I was attracted by it. It was also for that reason I bought my MacBook.
Will a prettier ubuntu attract more users my answer would be definitely YES.