'''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Dura Ace 9-speed cassettes use Ti only for the largest two (11T smallest cog) or three (12T smallest cog) cogs so, unless you spend an inordinant amount of time in the lowest few gears, they shouldn't wear significantly and will probably outlast the steel smaller cogs used most of the time.
Large cogs are inherently more durable than small ones since the load is shared among more teeth. Thats also one reason why chainrings last so much longer than cogs despite being made of Aluminum.
The really fragile cassettes are the Campy Record all-Ti cassettes which use Ti for the small cogs too.
The fact is, Ti cogs will last about 1/2 as long as steel, but everyone uses different cogs more frequently, so the ultimate life depends on how much each cog is used. As an example, I do a lot of climbing in the Colorado mountains. Using a triple, my most frequently used cogs were the 19 and 21T. I wore out the 19T steel cog on one cassette in 6,000 miles, but another cassette ridden on the same routes, had both the 19 and 21T worn severely after only 4,000 miles.
After that cog wear problem was recognized, I never bought another cassette with Ti cogs. I also found that you can maimize cassette life, by alternating the use of 3-4 chains, so a new chain is never installed on cogs with much wear. That's what results in chain skip - a new chain on worn cogs. That same worn cog with a chain having only a few hunfred miles of use will not skip.
Dura-Ace cassettes seem, to me, to wear a lot quicker than the Ultegra ones. If you have a sponsor buying you new ones when you need them, by all means race DA, but Ultegra really seems to be the sweet spot.