I have a DA cassette on one of my bikes. That cassette was on the bike when I bought it used. I'm guessing it had a couple of thousand miles on it then. Since then I've put about 12K miles and four new chains on it since then and it still shifts great. I will ride this bike in the rain, but I do keep the drive train clean and lubed. And I'll take the cassette apart just about every month for a really good cleaning.
When it is time to retire the cassette I'll probably put an Ultegra on. The DA is a lot of $'s more for very little improvement.