Joe,
A question I consistently ask our users is whether they’re using the Visual JSP Designer (does not matter if the design page is hidden) or the source only JSP editor.
1) If you are using the former, can you use the source only editor and see if that gives you a better editing experience? To use source only editor, bring up the context menu on the file and choose Open With > MyEclipse JSP Editor.
2) Additionally, can you clear your error log file (you can do this in the error view) and observe if any errors are logged as you see slow downs in typing?
3) After you do experience the slow down, does reopening the editor fix it? If not, can you open another JSP file, is that slow too?
4) Is this file particularly large? For us to get a rough idea, how many lines of code are in the file? Do you experience this issue with other JSP files too?
I apologize for the inconvenience caused, I realize this is a long standing issue; we are in a position now to address it, these questions will help us focus our search and analysis.