I use 10.04 LTS on work machines (by which I mean, machines at my workplace) simply because things stay the same on it and I'm not going to get calls saying "this huge colourful bar has appeared on the left of my screen, what on earth is it, and furthermore where on earth is my Thunderbird menu bar?". We have a lot of older users who are not especially computer-literate, so an interface that doesn't change is valuable to us.
The machines are also fairly ageing, and don't support the composited desktop. I did test Ubuntu 11.10 beta on one, but it was so slow (with what I assume was Unity 2D) that it would be unusable for day-to-day work. All we use at work are Chrome, Thunderbird, OpenOffice and Audacity - why would we need Unity? Why can't we turn it off?
For me, Ubuntu definitely peaked at 10.04 and I'm going to be looking elsewhere in the near future.