There are (at least) two issues here: The spaces bar itself, and the tabs.
I don't have a strong opinion on the spaces bar as such; though I don't like the use of icons-only rather than icons+text. They're a bit too vague, and require too much mental effort to figure out. This is especially true due to their monochromaticity (sp?) . The lack of visible text ("Calendar", "Tasks") is perhaps a benefit of the current two buttons for Tasks and Calendar - but only in that it makes it easy to ignore them... if you do want to be aware of them, then the text is missing.
Of course, if one does go with Icons+Text, then the spaces bar becomes pretty large, and may no longer make sense. A couple of other possibilities:
- Change the menu layout, so that one of the menus has these navigation commands prominently at the top. Perhaps like the "Window" menu in other applications.
- Have spaces be a toolbar which can be placed either to the right of the main toolbar, or at the left, right or bottom edge of the window; and like other toolbars, allow the choice of icons, icons+text or text only.
The other point is that I really don't want the address book in a tab! It's important that it be in its own window. I am also kind of skeptical about Tasks in its own tab, because it seems like too much real-estate for tasks rather than combining them somehow with some other content. But - I don't have any intuition about what I would do with Tasks exactly.
There is also the 'Home' tab. I don't see how that's a good idea. That seems redundant.