So this was on sale in the App Store, and with it I went from 40 MB free to 800MB free. Not too shabby! I wonder if it's on sale because it is irrelevant once Lion comes out or something...that would be sad.
Lion doesn't handle memory any different from Snow Leopard. That being said, there's practically no difference between "Inactive Memory" and "Free Memory" in OS X, therefore the app will yield virtually no boost in performance.
I have a MacBook pro that had limited memory and I often open many applications, so there is a lot of memory swap.. That being said, performance drops dramatically, and even when I close the applications the system performance doesn't always return. After installing icleanmemory, it not only lets me know when I am getting low on memory, it clears the memory and I have noticed better performance afterwards.