That AMD's offerings are on par with Intel's really isn't news. But it's a good bet that AMD is right when you look at consumer applications as a whole. The campaign goes to such extremes that it even implausibly claims that you need a Pentium III to get the most out of the Internet. Game Gear I'll start with games, because that's where SIMD will make its biggest impact in the short term. The speed-up is quite real.
Mileage varies, however.
Realize that many developers are only now getting a chance to optimize their applications from the ground up for dramatic improvements. The overall performance gain would only be a few percent. This effectively mitigates the impact of the new instructions on many current titles. This will change with the next generation of games slated for later this year and early next. For example, Rage's forthcoming game Dispatched, which is due in about three months, depends heavily on the CPU to render its complex, finely detailed imagery.