Personally, I use a subset of UML for most every software project I'm on. I rarely go so far as to build sequence, class, and use case diagrams for everything, but whenever I get even the slightest bit confused about something, I jump on a whiteboard and throw together a little model (sometimes transferring this to rose if I think this model will help other people understand the issue)
For simple Web apps not using any persistent components, I use UML but not many of my collegues have. Rational has put forth Conallen's WAE to help describe the web world in OO terms, but IMHO he misses the mark, leaving web people on their own for UML development. I've put together some techniques for dealing with this mismatch and I have taught it in courses and seminars, but a huge majority of web developers don't use UML for plain-old-webapps.
For EJB projects however, UML fits right in, so I see it in use a lot more often.
However, across the industry, UML isn't used nearly as often as it could or should be. People have this "ooga booga" fear of diving into UML and being swamped with thousands of useless drawings to maintain and archaic processes to wade through. THAT ISNT THE CASE. But, the fear is there, and/or people don't understand how UML can be a streamlined communication and rapid design tool.
I've worked in 20,000+ person multinational corporations, 4 person startups, nonprofit groups, and local governments, and the larger the codebase / software development team, the more likely people are to use UML. However, even on tiny projects with 1-3 developers, UML can be used to the advantage of the project (I have a UML activity diagram open in another window for a project me and two other developers are working on).
I hope that helps.. email or reply if you have more questions.