Kent, thanks for your report! It is quite strange and I would need more information from you:
1) Are you able to reproduce this behavior every time? (If yes, it will make things easier)
2) Please, fetch bzr version of GTG and try to play with it. Run 'scripts/debug.sh' with empty task set without any plugins... Is there still this problem?
3) How many tasks/tags do you have? I have quite heavy task list with about 500 tasks and it work for me without problems
4) Which plugins do you use? Try to turn it on/off and see if it helps or not. I made changes to notification area and it can consume more memory but not few hundreds MBs
5) If you find out, it is because of your special tasks file, you can use our anonymizer ( scripts/anonymize_task_file.py ) to share it with us for debugging
In other words, I am not sure what makes GTG so slow, we have to find out together.