I haven't gotten the Tunebuds Mobile yet, but I've had several pairs of the EarThumps / Tunebuds / whatever they changed the name to (i.e. the ones that have no microphone). I've never had a pair crack, but if I use them for running, it's fairly common that in about a year one of the channels fails. Once in a while I call them and ask for a warranty replacement and they're very nice about it.
But to be honest, I consider these amazing disposable earphones. They work great, you use them for a year and let them get all sweaty from running, etc, and then you get a new pair. The non-microphone pair can easily be had for $13 shipped on eBay -- $13/yr to have new headphones every year is a great deal to me. Much better than trying to make a pair of $100 earphones last through four or five years of running.
I'm curious about the tunebud mobile's but I have not ordered a pair yet. I can vouch for the headphone component though -- they're really quite good considering their price. They're very bassy, but they come with several sizes of ear grommets to get a good fit, they do a good amount of passive noise isolation, and they sound reasonably good.
If I can find a reasonable price on the miked version, I'm definitely getting some so that my current tunebuds can go 100% to my running iPod and I can use the new ones with my iPhone....