On the other hand, I did use it in combination with other techniques to provide some real information. At one point I had a hard-to-even-track kind of problem, with difficulty even looking for common trends. I created a help form for the user. Please fill out when this occurred, where you were (this mattered), what OS were you running, what browser, and so forth. What I found using the UA (and backed by other tricks) was that many users, young users who were enrolled in college, were not only unaware of their browser or operating system version but the OS itself.
Its utility began its decline when the browser makers began copying one another wholesale. It's kind of a shame. Capability-testing is better but for some troubleshooting applications, having something particular to pin your problems to is handy.
You should still get this information, but more privacy oriented manner.