Thanks for the suggestion about Gantt charts, David. I'll consider it for future enhancements to the product.
I'll investigate the freezing issue when editing on the iPhone 3GS, thanks for the report. It may be related to specific task data - or does it happen with any task? To avoid having to uninstall/reinstall, you can probably just "hard quit" the app instead to get things working again.
To hard quit, double-tap the physical home button on the phone to bring up the tray of open apps. Long press on GQueues and tap the red close button that appears.
-Cameron