It'd be really nice if refresh_folder_list could keep track of which folders in the tree you've got open and keep them open if they still exist after the refresh -- I refresh my folder list a lot because I'm using git to move between branches etc.
Also, could you make it so that the sidebar can be used with the arrow keys? I.e., I'd like to be able to select a folder, hit the right arrow key to open it, press up and down to select different files, etc.
Tabs: They look sweet, and as I said I'm a huge fan of the fact that you can drag them out into new windows. However, I just wanted to let you know that someone out there still likes the sidebar.
I have a widescreen monitor, so I'd rather take up room on the side than on the top (tabs leave me with fewer lines of code showing!).
There are a couple things that would make the sidebar totally killer. Chief among these would be adding the drag-out-into-a-new-window functionality that the tabs have. The second thing I think would be sweet to see (I think I might have mentioned this, but because I'm making this list I guess I'll put it here too) is the ability to act on a selection of multiple sidebar items: close all, drag all out into a new window, drag all to a new group, etc. The last thing I'd like is if there were a sidebar highlight for each group's frontmost buffer instead of just for the active buffer (i.e. if the front buffer in group 1 and the front buffer in group 2 were both highlighted). This way I wouldn't need tabs at all—I have them on right now mostly so I can see instantly which file is open in each group.