Re: Photoshop extended
If you only will ever use it for Photo editing, then stick with Photoshop standard - it does have the complete tool set there.
I've got CS3 extended. It was introduced because photoshop is making its first steps into the world of video. Its now possible (although the world hasn't quite woken up to this quite yet) for retouchers to use their skill set editing video - introducing its unbeatable tool set into an area which sorely needs it. Eventually I would predict, replacing 'high end' digital film editors. In much the same way, for still frame retouching Photoshop replaced systems like Barco Creator that were still hung onto mainly because they were unfeasably expensive, by a particular retouching community that couldn't see the light of day until it was almost too late.
Its 3D tools are still at a relatively basic level even in CS4. But if you do visualising, as I sometimes do, for a living it can be a time saver to have moveable 3D objects within the photoshop workspace