Personally I'm pretty frustrated with the way it works. I've noticed all of the following , and at least some of these apply to dev tools too. I don't like the way Google controls the internet with Chrome, but at least its dev tools just work.

• Sometimes when I try to use the element picker tool it actually clicks the element instead of selecting it in the toolbox
• I can't change selectors in CSS files in the sidebar, I have to go the style editor (Chrome lets me do this)
• I can't easily copy HTML attributes, if I double click on an attribute, the text is selected but when I press CMD C, it copies the entire tag with all of its attributes.
• A lot of the time CSS properties I write just don't apply and isn't crossed out. Its like it just has a hard time doing that.