Just a code Snippet and three files to improve the (broken/too small/impossible to catch) UISlider from Apple.

CGRect rect = CGRectMake (16.0, 262.0, 284.0, 35.0); //last size of cgrect is important : thumb is 34 pixels high
accuracySlider.frame = rect;
UIImage* thumbImage = UIImage imageNamed:@"thumb.png";
accuracySlider setThumbImage:thumbImage forState:UIControlStateNormal;
UIImage* leftImage = UIImage imageNamed:@"left.png";
leftImage stretchableImageWithLeftCapWidth:5 topCapHeight:0;
accuracySlider setMinimumTrackImage:leftImage forState:UIControlStateNormal;
UIImage* rightImage = UIImage imageNamed:@"right.png";
rightImage stretchableImageWithLeftCapWidth:5.0 topCapHeight:9.0;
accuracySlider setMaximumTrackImage:rightImage forState:UIControlStateNormal;

And the images:

Bigger ah?