Always Keyword Stuff Intelligently
Googler, Matt Cutts publicly outed a spammer using a text box to keyword stuff his webpages full of keywords. Whether or not Google can detect the gimmick of using tiny text boxes as a means of lamely hiding text on a webpage is totally besides the point. Adding hundreds of different words to a webpage, whether visible or invisible, would only decrease the keyword density of each of your keywords close to zero.