Whats up with those gloves I see some yo-yoers wearing on one hand?
Those gloves allow the string to slide easily over the fingers of your non-yoing hand, which facilitates many tricks. In addition the string can rub and cut the fingers of your non-yo hand, especially in humid weather. In that case wearing the glove protects those fingers from harm. Bear in mind that these gloves are generally worn on the non-dominant hand (left hand for right handed yoers, right hand for left handed yoers). Some yoers do wear one on each hand, but this is not usual. Additionally products have come out recently to provide protection for the yo hand (Finger Armor, Hyper Yo-Yo Glove).