I posted a module today that will be of interest to anyone wanting to use tabs on their site without having to do custom coding.
It's called Panels Block, http://drupal.org/project/panelsblock. With it you can expose a set of panels as a block via a new option on the panels edit form. (Only the content added to the 'left' area is made available as a block.) There are two ways to display the content: default (sort of like a regular panel) and tabs. (The tabs.module, part of Javascript Tools, is required.)
If you select tabs, you get the content you assigned to the left area in the panel in the form of tabs.
And, because the panels are now a block, you can add them as a block to a different panel. So you can easily create a panel with, say, three sets of tabs (each tabset being a panels page exposed as a block.)
I wrote this today, so it's fresh off the press and no doubt has some wrinkles to work out. Please post issues or patches on the module if you have ideas of how to improve it.
One thing I'd like to see is a couple of additional options beyond tabs and default. 'collapsible' would make each of the panels content pieces collapsible (like, e.g., collapsiblock does). 'accordion' would apply an accordion effect.