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Well, for 92 % of them. A lot of people disable JS these days. They get tired of pop ups, redirects and other JS abuse some designers use. For about 8 % of visitors, the spam is obvious.
I would not play with such tricks. The competition may react to it.
Like most SEO guys and galls, I use Opera to analyse competitors, it saves me a gazillion clicks a day just to switch between a JS and non a JS support for the browser.
I report any irregularities to my clients. If the client decides to blow the wistle to SE about the competitor using such cheap tricks, I provide him all the URLs required, for a very small fee.
Bottom line is, dont use quick fix stuff, it's risky, spammy and passé.