Evolution of Photoshop

Here's a simple list of the major features of Adobe Photoshop throughout the years:


1
1990
Following Thomas & John Knoll's licensing agreement with Adobe, the first Mac version of this "Killer App" arrived in February 1990.

2
1991
Version 2, code named "Fast Eddy" arrived in the summer of 1991. With the arrival in 1993 of version 2.5, the application now also supported the Windows platform.

3
1994
This version added for the first time the "Layers" feature.

4
1996
Controversial key commands were changed.

5
1998
Version 5 introduced colour management and the history palette. A major update, version 5.5 bundled Adobe's package ImageReady in an entirely new iteration, giving Photoshop excellent Web specific features.

6
2000
The entire interface was overhauled. The new design accommodated better organisation and more efficient use of palettes.

7
2002
The healing brush and patch tool were added.

8
2003
Known as Photoshop CS, Photoshop was now presented as part of the Adobe Creative Suite. While on first glance not much appeared to have changed a large number of new features were added, such as RAW support and the histogram palette.

9
2005
Known as Photoshop CS2, the latest version includes a bunch of powerful new filters and editing tools, tighter integration with and support for Illustrator graphics, support for 32-bit images, and significant improvements to its camera RAW workflow.


From other websites I can gather that CS3 had Clone Source palette and nondestructive Smart Filters introduced. This was also the first version able to import 3d objects , but with limited editing capabilities. However Cs4 changed that and you can directly "paint" on meshes in the program.

http://www.hongkiat.com/blog/evolution-of-photoshop/

The link above is a neat compilation of screenshots of several versions of Photoshop. I first started using the software when version 7 came out in 2002. By then the software was already fairly advanced and going to higher versions didn't seem like a steep learning curve.