Xcode finally added tabs but the problem is that they behave very strange. For example they will keep a tab open only if it was opened to a new tab.
If you open a file just by clicking in the project tree, Xcode will close your tab as soon as you are clicking on another file in the tree.
Is is possible to make them behave like real tabs and prevent Xcode from reusing them? How?
UPDATE for 2020:
Finally, almost 10 years later, Xcode 12.x now appears to mostly resolve the issue described here. There is a new Navigation Style option in the Navigation settings panel that controls this behavior.
The behavior has some new quirks/design-choices that seem to make sense, but I'm still getting used to the new experience. For example, a tab will get re-used unless the file in that tab has been edited recently; such a tab is indicated with an italics title.
PREVIOUS ANSWER
I don't think you can currently get the behavior you desire (or I desire). While the tabs work like Safari, they don't work like tabs in other popular IDEs (Visual Studio or Eclipse). And for me this kind of sucks.
In general, I expect IDE tabs to keep more than 1 file open. So if I click a file in the project tree, I expect that it will switch to the tab I have opened with that file - if I have already opened it. Instead, XCode 4 changes the current tab to the file I clicked - making 2 tabs with the same file. Having 2 tabs with the same file is fairly useless.
This forces the user to scan the tab bar first to see if the file is currently opened; if it's not opened then you can look to the project tree. But if you click in the project tree first (which is what I tend to do) then you get punished because you will have just killed a tab.