For the first time in my 25 yr Mac experience, I skipped installing a new OS when it was released and gave Lion a miss.
One reason was that developer machines are becoming too critical to blindly upgrade, but it was primarily because I didn't want some of the major changes imposed on the user before fixes or applets were published to make it more adaptable.
However, the way things work I know it will be inevitable sooner or later and e.g. a new machine will bring in Lion, proper syncing with iPhone will require Lion eventually etc.
I have 2 macMini servers running OSX Lion Server (smoothly, I must say) but those machines are left alone most of the time and are a poor comparison for day-to-day use.
I would be curious to read any positive / negative experiences from other developers currently working on OSX Lion as their standard machine.