From a teachers perspective our competition is tough. Passing out a handout of 30 problems that are all in a format of 534x25= is not as stimulating in the students eyes as playing games such as Grand Theft Auto and Resident Evil. Granted, that will always be a tough uphill battle for math to win out over most video games, but the point is, students today are much more immersed in technology than ever before. So even if you need to pass out a math worksheet to review concepts and formulas, it will greatly benefit your cause if you design the worksheet to be as stimulating as possible.
Quality vs Quantity,Some free worksheets are not good quality - the pictures are fuzzy, backgrounds print grey or speckled - and children tend to notice these things. If you are using the worksheets to educate your child, you may want to choose good quality worksheets that encourage your child to produce good quality work. After all, its a little difficult to ask your child to color within the lines and work neatly when the worksheet they are filling in hasnt done the same.