I used to play with my customized skin which actually started from wario ware skin but changed alot of the time, and even did my own skin on this p/2917930#p2917930 . But now i use default skin since 2 months ago since it doesnt affect gameplay at any shape or form for me. I am playing as well as i used to without much difference. Not even insibile 300s xD
Sometimes custom skins and skins from the site make it more difficult to play by having a cursor which tends to blend in with backgrounds, and having hit scores (50, 100, 300, etc.) which are so big that they interfere with visibility, not to mention that some of them are kinda flashy. The default doesn't cause any problems for me so I just stick with that.