I'm using Yahoo Web Mail Plus (trial version) and would like to make a few observations.
1) The first column in the web interface (the one with the folder list) could be wider. Ideally, you could change its width by dragging its right edge.
2) Some options are difficult to find (see "Settings").
3) The account selection was better in the previous version.
4) The toolbar that appears when selecting a message could be wider and should also display the print function. Ideally, the toolbar could be modified by dragging the function icons.
5) When moving messages, automatically focus the search box without having to click it.