This is a topic I'm particularly interested in, because I actually do not like tabs for most situations. I think we do sometimes fall back on tabs a bit because it's an easy and common option to present more information in less space, rather than perhaps thinking around the problem a bit more and understanding the user's relationship with the data.
In general if we do our job properly then after looking at the requirements and understanding how users will interact with the system, then we should have all the necessary information to be able to determine for a given scenario whether tabs are the right way to represent sets of data or not.
Typically we end up implementing tabbed content because we are interested in only one page at a time. Tabs, by their very nature, hide all other content, so if a user is likely to keep needing to refer back and forth between tabs, or is going to sequentially move through all the tabs, then tabs are not the right way of presenting the data because it doesn't make things very easy for the way the users work - in fact it can be downright awkward. I frequently see users of software trying to manage ever increasing numbers of tabs of data and flicking back and forth trying to find the one that has the information they were looking at earlier.
If there is linkage or relationship between the pages of content then either the number of tabs must be reduced or alternative presentations should be considered - or alternative mechanism of accessing the content (hierarchy, favourites, historical, most popular, etc depending on the application in question).
If the tabs simply present sequential information, then tabs are not appropriate either because the criteria for splitting data at one point or another is less well defined or does not help to categorize the data in a clear fashion - you wouldn't present pages of a book using tabs - you wouldn't present pages of search results in tabs.
If there is no linkage or relationship between individual pages, then tabs should generally be fine. So for example in a browser, tabs are good - they divide separate areas of content - although having said that, actually if you really look at how people would like to organize their browsing sessions there is even life beyond tabs - eg Aza Raskin talks about Tab Candy for FireFox (aka Panorama or Tab Groups)