Yeah, single-window mode has been in the Finder for a very long time (wanna say since 10.1 or something), but compared to the OS 9 Finder it's always been a bit flaky and will sometimes forget window sizes+positions. I figure that it's probably never gotten the level of attention required to make it polished.

It's also missing the open folder indicator that the Classic Finder had, where folders that had their window open somewhere had a different icon (filled with a stipple pattern). This is a bigger problem than it sounds like, particularly with OS X having multiple desktops and making it easier to lose windows.