Having previously upgraded from CS3 to CS5 I was reluctant to purchase CS5 on the grounds of cost. Changing computer operating systems, namely Windows to OS X has meant an upgrade was now feasible. Photoshop CS5 is quite an upgrade from CS4. Some of the main changes for me are that Adobe Bridge can now be access directly in Photoshop, HDR has been been given a make over, and the filters have been vastly improved. I have to admit I don't manipulate my images a great deal so can only provide an opinion based on my actual use. What i can say, is that i am very impressed with CS5. Whether someone would upgrade from CS4 to CS5 really depends on your demands of the product I feel to justify the price or like me change operating platforms. If though you are a heavy user of photoshop I would seriously consider and recommend CS5.