Using KDE 4.5.2 on Kubuntu 10.10 with Oxygen style, but can be reproduced with other styles.
I have 3 widgets on my panel: Weather Forecast, Calculator, System Monitor
I resize them, but they do not remember it through reboots. Apologies if this is in the wrong section, or a bug report should be filed.
I assume that since none of the widgets retain sizes that it is not a problem with individual widgets. Also, it makes no difference if widgets are locked or not.

If you add a new widget is it saved when you logout? Sounds like your Plasma configuration may be damaged.

bcooksley wrote:If you add a new widget is it saved when you logout? Sounds like your Plasma configuration may be damaged.

Yes, all widgets are saved on logouts or reboots and otherwise work properly. If I have a widget on the desktop it works fine as well, the problem only happens when I embed them on the panel. They drop down properly, but after a reboot, return to their original (too small for me) size. For example:

The size of widgets within the panel is determined by the panel height. If you want them to be a different height, you need to put them on the desktop where you can adjust their height and shorten the panel width to accommodate them or add another panel and place them between the two panels.

Perhaps the picture added confusion or I didn't describe my problem well enough. I will try again in simpler terms. When you add a widget to the panel, it becomes an "icon". You can see I have 3 of them from the picture. When you click that icon, the widget drops down, like a menu would, and if you click the icon again, it slides back up or hides itself. When the widget is visible, it can be resized by grabbing the bottom right corner. Even Kickoff can be resized this way. This is my problem. I can resize the widget, but it does not persist through logouts or reboots.
Here you can see I have the calculator dropped down, and resized how I want it.

Ah. This may not currently be saved by Plasma. I can confirm this behaviour on trunk, although Kickoff saves it state, calculator doesn't. Please file a bug report at bugs.kde.org.

Perhaps related to Bug 243083. I filed a reply, but did not open a new Bug as of yet, but will follow this thread.
Thanks for the help. I would also remind you that this behavior is not limited to calculator, I also have system monitor and weather forecast widgets with the same problem. Interestingly enough, the Quick Access widget does not seem to be resizeable.