Also have the 60Da and love it.
As mentioned, the flip screen is very handy, also mentioned, live view(Cam back or tethered) is great for focusing, not yet mentioned is how handy the in-camera electronic level is for shooting nightscape or lightning shots, get your horizon right first time with no mucking around and best of all, when it's too dark to see the horizon!
As far as I am aware, this feature is only available in the pro-sumer bodies(1D's, 5D mkIII, 6D, 7D) and the 60D.
I am not sure, but Canon's blurb kinda reads as though the 60Da has a lower noise sensor than the vanilla 60D, hard to say tho as it's a bit vague.
Perhaps they pick the cream of the 60D sensors for the Da
Now, if canon would release a 6Da
