Though I'm not one to usually hop in here, I will say that when I first turned off mouse acceleration in osu!, my skill level jumped a lot. (Also: Default Microsoft mice that come with the computer.)
I play with normal mouse speed in windows and 1.3x in osu!, granted I'm not the best player, but I think I play pretty well.
Of course, like luke said... if you're already playing with it on and have been for a long time, you don't have to try to change it. However, changing MAY be able to get you even better at osu! after some practice.
Then again, it may not. that's why you experiment.