I've noticed that after updating a single task and pressing Save, the whole project Plan outline page refreshes. (eg: changing a task to 100% and Complete) This may not seem like an issue at first glance, but it breaks the code if you click on a new task to update before the plan outline is fully finished loading.
This normally wouldn't be an issue if you are just updating a page with 25 tasks or so, but when you get to a higher granularity and have something like 500+ tasks and you are updating multiple tasks you will break the code really often.
What happens: you update an item and click save, as the project plan is reloading you click on an item and select view/update, you update the item then click save, the update box changes to a blank page and the project plan page doesn't change.
There are really two issues at hand here:
1) Refreshing of the whole project plan (on large documents) breaking the update code. It would be nice to update just the one item on the page without having to update the whole page. Like how gmail updates the number of e-mails in your inbox - just the one line without refreshing the whole page.
2) Ability to update mutliple tasks at once - if this were possible, multiple tasks would be updated at once and the page below wouldn't need to refresh multiple times