Safari in DP 1 was pretty terrible to use. Horrible memory usage, laggy scrolling, unresponsive UI, etc.
But, Safari in DP 2 is pretty awesome. The scrolling is just so smooth! I can sit here and scroll all day. Even Verge which sort of lagged for me in Mavericks, is smooth, smooth, smooth! It's more responsive and it's taking MUCH less memory.
Oh and before I miss this important point: the scrolling is very smooth.
There are some issues still there though like the UI is still sort of lags, the tab view takes some time to get used to, and the animation for it is very slow. The animation for Share actions are very slow too. For example, if I tweet the current link, it takes a whole two to three seconds for the tweet sheet to even pop up for me. So far though, I've not had any crashes or anything.