This. Also, why does Sparrow or Twitter/Mac insist on inventing new widgets and putting buttons in the title bar and stuff. It really annoys me.

Apple themselves started moving the toolbar into the menubar (e.g. iTunes, Mac App Store).

IMHO the "left category bar" of Sparrow and Twitter for Mac are pretty useful, given that (a) screens are much more wide than high, and stacking everything in horizontal bars is a waste of space (b) they move "categories" from horizontal tabs to vertical, thus making the Y direction for 3-or-more finger gestures meaningful and intuitive.

iTunes is an abomination anyway, but the buttons at least look like buttons. Not so with sparrow, they are just darkish inset shapes. (Much like the Mac App Store, which, even though it's made by Apple, should not be used as an example for good UI, ever. IMO.)

Nothing against the left category bar, but why not use a standard widget? Think Mail or iTunes. Also, selecting an item from a vertical list on the left and changing content horizontally on the right feels strange to me.

This isn't an excuse, but I know that they use Titanium to make the application portable between all the platforms they support. I think some of bad UX experience on OSX is because of that.