It came in mint sets. Someone cracked it open then spent it. Depending on the grade they can go for up to 20 bucks. The W referse to the West point mint out of New york. I believe there were only 1.5 million of those mints.
These were the brainchild of Philip Diehl, then acting Director of the US Mint. They were intended to give something special to long time mint set buyers. These come very nice and gems are almost typical. Superb gems are not uncommon.
The attrition on these is likely rather high as they get "lost" in the mint set packaging and many people don't realize they are intended as part of the set. Many of them end up in the garbage stream for these reasons or in circulation. Dimes in circulation have a very high attrition due to their small size causing them to slip through holes such as pants pockets and their tendency to "float" on larger coins. They are more likely to be tossed in the garbage because of their low value and low utility. If one is dropped people are less likely to retrieve it. About 60% of the old clad dimes are gone now and about 20% of 1996 dimes. A very small percentage of the '96 dimes lost are W mint mark but the %age increases each year as more W dimes get in circulation.
Of course the primary cause of attrition for these coins is like almost everything made by man; fire and flood.
The '96-W got very little attention the first few years but has been getting more popular in the last decade.
Finding a 1996-W in circulation is a once in a lifetime find. Although they're very "common" in high grades, if I found one in circulation it'd be worth more to me than a brilliant example simple due to its provenance. It made a very interesting trip to get to your pocket. :-)
-Steve(GSNA R-2306) The Black Cabinet A Database of Counterfeit Coins. Counterfeit identification and attribution services.