The "workspaces" feature is at least partly broken, and there are bugs open which have been open for years, if not decades, suggesting or asking for improvements. But despite the weight of evidence that people want this improved, the Eclipse developers are generally more interested in adding the latest "gee whiz" features than dealing with "bread and butter" issues.

And, sadly, the UX aspect isn't even the biggest problem with Eclipse (all "IMO" of course). Performance, especially memory usage is a huge issue (especially on 64 bit systems) and the updater/plugin mechanism is too damn unreliable. If you use more than 2 or 3 plugins, it's almost inevitable that you will, at some point, try to update something and get the infamous "could not complete operation" message when adding a new plugin, or updating an existing one. Now, that's not really the problem... the problem is that eclipse just vomits a page and a half of error messages and opaque version numbers and strings at you, when this happens... instead of giving useful help on how to resolve the situation.

All of that said, I still use (and, in many ways like) Eclipse, but it is very frustrating to see these same problems drag on for years and years.