The "ticking" of a mattress is its outside covering. On a traditional mattress, this ticking is sewn. On many of the newer specialty mattresses (memory foam beds, air beds, latex mattresses) the ticking is a zippered cover.
In either case, one of the latest trends is to add a fancy ticking in order to position a mattress as a higher end model. The range of these upgraded tickings is huge. From silk and cashmere to Cool Max and other temperature regulating textiles, aloe or vegetable infused materials, and even tickings embedded with small magnets or elemental copper.
And all these claim to have some sort of benefit for the sleeper: silk and cashmere to help you sleep cooler and add comfort, aloe for its health benefits (although I have to admit I'm fuzzy on what these are), coolmax to help you sleep cooler (used a lot on memory foam beds), and the magnets supposedly to create a more "natural" magnetic field that is healing for sleep purposes.
Are these claims valid? Boy, I have to say I'm skeptical about most, if not all, these claims. First and foremost, most people use a mattress protector or mattress pad over their mattress to protect it. So people almost never sleep with their sheets right on top of the ticking anyway. I'm pretty skeptical that you continue to get the benefit of the aloe, cashmere, silk or coolmax through a 1/4 thick mattress pad. As for the magnets, I am just generally skeptical on the health claims here, although I'm not saying it might not offer a benefit (for some general information on this, Google "magnetic mattress therapy"). But how comfortable is it to sleep on hard pieces of magnets sprinkled throughout your bed?
Bottom line -- if you will be using a mattress pad or mattress protector over your mattress, you can save a lot of money by buying the same mattress (with all the same innards) and foregoing the fancy cover. I can't say you will always have this option, but in many cases there will be very comparable mattresses which differ only in the cover (and their price).