Yes, I think they have been releasing material at just the right pace. I've been able to keep up with the releases even with my other gaming and game related reading, but probably would not be if it was coming out much faster. Plus they've been doing a great job with supplementary support on their websire, and in Dungeon (and to a lesser extent Dragon), so fans hungry for more info have the ability to get a little more than what's coming out in the major releases.
More importantly, quality is far more important than quantity, and so far they've been doing a pretty good job keeping the quality up. I'd hate to see that trend reverse.