Enabling tabs in xcode? Or lessening the pain of not having them?

XCode 4 now supports tabs. You can enable by selecting "View / Show Tab Bar" menu.

Not really, but one alternative is View > Show Favorites Bar and drag five or six frequently-used source files into it. Not as flexible as tabs but satisfies your request for "quickly navigate through a subset of files".

The traditional way is to use the detail view. Get the files you want in the Detail view by one of these means:

• Put them all in the same group, then select the group
• Enter a filter expression in the Search Bubble that narrows the items shown
• Define a Smartgroup that includes just the files you want
• Get a list of the files as a Find in Project result, then select that item in Find Results

Then you can use the Detail View as your list of interesting files and navigate through it quickly with the up and down arrows.