This is too good of a google+ thread to not share LINK
If you don't want to read through, here's quick summary:
**Do not wrap your managers in using statements
using(DynamicModuleManager manager = DynamicModuleManager.GetManager()){
//Code
}
Why?
Everytime you get a manager, sitefinity stores it for the duration of your http request. If you dispose it in a using statement it'll be disposed when that statement completes so the next control\widget that tries to use the manager will have to create a new instance of it (instead of just using the existing shared one).
Think of it like a bucket full of managers