Yes, my boss makes me, I generally have to give a presentation and talk nicely to the customers.
Mileage varies, but generally its an opportunity for the users to talk to each other and become more aware of what the products can do - as one customer uses it for one task that others may not have thought of.
We also show them upcoming features so they have an idea of what their upgrade money is buying, and have the opportunity to ask the awkward questions, and suggest changes before the product is 'finished'.
We may be different in that we actively engage with our customers and expect them to be more involved in the products as a whole, we want them to use it to its fullest capability and help them do their work better. I've been to a few user group meetings for other products (generally 'finished' products) where the UG is simply a marketing exercise to get you to cough up the cash for the new version. Free food and half a day out of the office are possibly the only reasons I've gone to them :)