The most remarkable thing is that you never have to drop to a command prompt, unless you want to. All of the linux infrastructure and tools are there, but it's all been abstracted away with a nice clean GUI. For the first time in my life, I actually prefer using X over the shell for managing my machine.
It's also amazing to look at how rapidly Canonical is improving Ubuntu. Every six months, I get more functionality and new software, with an improved UI and fewer rough edges. I'm anxiously awaiting 10.04, and I know that 10.10 should be another big improvement. That kind of predictability is nice.
I jumped ship from Linux to OS X nine years ago, when OS X 10.0 came out. I hated wrestling with X, battling device drivers, and constantly missing basic functionality. All those problems are finally solved, and I'm back on board. 'Desktop Linux' may never happen, but 'Mobile Linux' is definitely here, and it's pretty darned cool.