First Sidewise is the best thing since sliced bread. Stylistic quibble though for Mac. It's Mac style to be able to click just once to select an item before moving it, e.g. in Finder. Discombobulates first time Mac Sidewise users. :} We do get over it.

Is this relevant?

http://sidewise.userecho.com/topic/123277-very-nice-one-question-would-it-be-possible-to-implement-focus-follows-mouse-on-a-mac-at-the-moment-one-has-to-click-first-to-get-the-focus-to-the-sidebar-windows-and-only-then-can-one-click-on-the-desired-tab/

(I don't use Mac, so I don't know.)

Yes, that did indeed prove to be relevant, thanks.  Solving that matter should solve this question.

To clarify, does this accurately describe the situation on Mac?:

• When the sidebar is not focused, clicking an item in the sidebar only focuses the sidebar; a second click is required to then actually select the item
• When the sidebar is focused, a single click on an item immediately focuses it

Yes, Joel, that sums it up accurately.

If there was an option that automatically focused the sidebar when the mouse hovered it (and probably also w.r.t. the docked-to window), would this alleviate the double click problem also?

Indubitably, the focus follows mouse onto the sidebar would fix it, yes.