There's little doubt that the iPad has revolutionized the PC industry, ushering us into a "post-PC" era. But while sales of Apple's iconic tablet are still robust, there are signs that they may be softening. If you dig into the sales numbers Apple issues every quarter and look at them over a longer time-frame, you have to wonder what slowing iPad sales could mean for the company moving forward.Good news, bad newsWhen Apple introduced the iPad in January 2010, the rest of the tablet industry was miles behind. Despite months of rumors about the forthcoming product, no other tech company was prepared to match Apple's sleek, $500 creation when it launched. Early Android tablets like Samsung's Galaxy Tab and Motorola's Xoom were critical disappointments and commercial flops. When Google finally released a
