Ubuntu 13.04 Final Beta
came out today. I was already on the dailys for about a week now. There were some glitches initially, but it seems to have settled down nicely. It took some doing, getting it to look the way I wanted, but it's pleasing to use now. It's fast enough, though Linux Mint Cinnamon is faster on my computer. Not terrible at all, though, on speed and resources. I always thought Ubuntu was a little clunky, but it started improving with 12.04 and 12.10, and I agree with the OP it's come a long way with 13.04.
I have one complaint, which is the connection to streaming goes just one bar, using Amazon in Firefox, and the same extreme slowness is suffered on Netflix desktop. I know the Netflix desktop is installed properly. I use it on Linux Mint 13 Cinnamon, Lubuntu 12.10, Voyager 12.10, and Elementary Luna Beta1. They all stream properly. So I think this particular problem is with Ubuntu 13.04.
I don't know if I'll keep 13.04, but it is quite nice.
Update: Out of curiosity, I replaced Lubuntu 12.10 today with 13.04. There is no connection problem with streaming.