Problem 1 :
maybe it's an issue due to mime type definition, or possibly an interaction with some plugin.
I do not face this issue with any of my browsers : FireFox (Win XP and 7), Chrome (Win XP and 7), IE 8 (Win XP) and IE 9 (Win 7)
Do you face such slow issue with IE8 on the Demo :
demo.projectorria.org ?
New Problem 3 :
I do not face such slow actions with different browsers.
What is sure is that IE8 is really very slow.
You'll possibly find it very slow on planning view.
IE9 is much better.
FireFox is quite good but may face some memory leaks.
Chrome is my favorite : quick & fluent.
I hope than with many users on a server, the slow time will not increase ?
I made some performance testing with about 100 users simultaneously working, and performance is still quite good (with a good machine).
I also had tests with high volumetry : 10000 activities, 1000 projects, 1000 resources, and after some improvemnts, performance is quite good.
You may find performances test result in the forum, I posted it.
New Question 4 :
No, parameters are in the database and in a specific file that is never erased (never delivered). So you will not loose any parametring or data.
As you correctly guessed it, php code changes can be erase if you don't save it, that's all.