Version: (using KDE KDE 3.5.5) The tooltip for directories shows incorrect size values. It seems it sums the files inside a directory, but only 1 level deep, not recursively. The problem is present in the tooltip shown when the mouse is moved over a directory icon, and also the tooltip bar of the window shows the miscalculated sum of the contents of the current directory. I know recursive scanning of a directory can take some time, but even a one-level listing can take an arbitrary long time, so I don't see any real difference. Also see relevant bug 48434.
I think I've misunderstood bug 48434, this is probably the same bug, assuming that the algorithm calculating the size of a directory is the same for both tooltips. Additional notes: If the contents of the tooltip can be updated after its shown, please make it contain the total size of the directory and that number should be progressively updated, just like in the properties dialog box of a directory. If the contents of the tooltip can't be updated, than it is probably a bad idea to wait with showing the tooltip until the recursive size calculation is ready. In that case it should show the size of the directory entry, but not the current false number which confuses the user. Remark: The detailed view could also have a total size column.
Regarding tooltips, I think that could get very resource heavy. A nice idea, but impractical in my opinion. That said, the idea about having the detailed view show the total size of folders is great. I'd like that very much, and it would provide a feasible workaround for Bug #156249.
Another similar wish is bug #158090 .