Although this tip isn't necessarily recommended for everybody, it can help you make your system faster. The default 'Oxygen' widget style can be heavy on its resource usage despite from the fact that it has been made faster over the years. Depending on your visual tastes and system hardware configuration it might be worth the effort to pick alternatives like Cleanlooks, Plastique or QtCurve.

You can change your style under System settings > Application appearance > Style.