I have paid for 1Gb of space on my iDisk before the upgrade of everyone to have 1GB of space. I was a little worried that I would be credited for the extra money that I paid for the space. When I checked the .Mac preference pane, It said that I only had 1GB of space available.
When I went on to the .Mac page, and viewed my Storage settings, it had additional options to allow up to 2GB of space available. (Unfortunately, the current selection was on the option that gave the greatest space to my iDisk.) I easily fixed that problem, by selecting a different setting, and then reselecting the largest setting.
Now it appears that I have the whole 2GB available. There a small cosmetic bug though. In the .Mac Preference Pane, it shows the maximum space as 1GB, even though the middle of the bar represents 1016 MB.