I bought about a dozen meerschaum pipes, when I was stationed overseas during the early 1980's. I've given a few away over the years, but I still have 7 or 8 of them. Many of them are still un-smoked, but the ones I have smoked are coloring nicely. Small ones can color fairly quickly, but the larger ones take decades. They start at the shank, and the color moves slowly forward, patients is definitely needed to get a big one to finally show its color.
They're an interesting pipe to smoke, they have a lot of aesthetic value, as well as the fairly neutral addition to the smoke. However, a well seasoned meerschaum, will add more and more flavor to the smoke. They also get much harder as they absorb the tars, turning from a brittle, easily broken pipe, to being rock hard. I thoroughly enjoy smoking a meerschaum pipe, but certainly not to exclusion. I love my briar pipes equally well.