While SteelSeries is promoting the view that DPI is irrelevant for gaming mice, Razer president Robert "Razerguy" Krakoff raises his voice that DPI does matter. You can read Krakoff's opinion over at ARS Technica.
"I think gamers care about DPI and I do think the term makes sense for today’s mice. We pioneered this industry back in 1999 when we came out with the first gaming mouse offering 2000 DPI—at that time gamers were told by our competitors that 800 DPI was enough," Krakoff told Ars. "Now people are saying 1600 DPI is enough, just like there were “purists” who believed in silent movies, black and white TV or perhaps film rather than digital cameras. By the way, I could discuss CD vs. vinyl for days."
The other issue comes from the price dropping on larger screens and video cards. As resolutions and screen size go up, so does the demand for a high-DPI mouse. "There are also more high-sense gamers around now, corresponding to the much larger screens and much higher resolutions available," argued Krakoff. "Many of the features Razer pioneered are being used in all gaming mice in the industry today, just as you will find high precision DPI metrics being used by pretty much all gaming mice out there."