Michael Pineda is a 22-year-old Major League rookie who's never before thrown more than 140 innings in a season. So this should come as both reassuring and obvious news: the Mariners plan to keep a close eye on both his pitch counts and his innings total over the course of the year. Carl Willis and the organization haven't yet set specific ceilings for either, but Pineda will most definitely be handled with care.
We saw the Mariners take things easy with Felix Hernandez for a while before letting him loose, and based on a sample size of that one experience, this should all work out swimmingly. Of course, there's no way for anybody to know what Pineda's physical limitations may be - he may be weaker than average, or stronger than average - but I don't think anyone's going to argue against easing him in a little bit. Taking advantage of off days, limiting pitch counts, maybe shutting him down in the middle of September - there's little reason not to do these things with Pineda in a Mariners season that doesn't look like it's going anywhere good. With young pitchers, caution is a virtue, even if it doesn't always work out.
One wonders how the situation would turn out in the event that the Mariners made a surprise run for the playoffs. Presumably, Pineda would be a big part of such a run, and the Mariners would want to keep him pitching. But then, last year the Giants and Padres leaned heavily on a 20-year-old Madison Bumgarner and a 22-year-old Mat Latos, respectively, pushing them beyond their career highs for innings, and they've both gotten off to rough starts in 2011. One could argue that a competitive Mariners team this year might in some way put Pineda's development at risk.
Fortunately for Pineda, Mariners.