Eclipse has a long history of behaving very badly when editing anything that looks like XML. In some cases, it would indicate errors that weren't errors. In Juno's case, it mostly seems to involve sluggish response, and especially when doing Find operations where the Find dialog takes forever to respond.
You can get better performance by opening the file using an alternative editor (right-menu selection on the Navigator). You lose the intelligent editing of the HTML-specific editor, but you'll get to go to lunch an hour sooner.
An IDE is no substitute for an Intelligent Developer.