There were a lot of complaints when we decided to limit the size of icons placed on panels in plasma to 32×32 pixels.
The reasoning behind limiting the size were requests from users who use vertical panels – vertical panels are usually made wider then standard panels, and icons would grow to 300×300 pixels taking up most of the space on the panel.
Putting a maximum size for icons was a good decision generally, but the bad side of it was that the new size was hard-coded. There was an option in the system settings to change sizes of icons, but setting the size for panel icons was disabled.
Now, thanks to a patch by Mike Kasick, this option is enabled and it works. Mike is one of the best types of users – although he isn’t a Plasma contributor (as far as I know – no SVN account) he sent us a patch, and responded to all of our suggestions with revised versions.
In the end, Aaron and myself adapted the proposed patch a bit to better fit the rest of Plasma, and it entered the SVN so it is on its way to KDE SC 4.5.
In KDE SC 4.5, the option is located in System Settings -> Application Appearance -> Icons -> Advanced -> Panel