I have always been skeptical regarding apps which claim to accelerate a Mac, or which claim to recover fragmented memory. One reason is that a Mac will naturally regain most of the lost memory after using a memory hog, if given enough time to do so, even if you don't reboot the machine.
Not only that, but a computer can't operate any faster than its actual clock speed. It may seem to be accelerated if you use one of those apps which rely on adjusting the nice parameter of your running processes, but it is basically an illusion. All you are really doing is giving the forefront app more processing power, while denying it to the rest. That isn't real acceleration.
Nevertheless, despite the aforementioned reservations, yesterday afternoon I downloaded and installed the free version of Memory Clean on an early 2009 24" iMac with 4 GB of RAM, in order to determine if it really lives up to its claims.
After letting it run for perhaps three hours yesterday, and seeing how it performed -- manually using the clean option does in fact regain a certain percentage of fragmented memory -- I decided to take the plunge and paid the $5.00 for the more advanced extreme clean version.
Folks, I can tell you from firsthand observation that there is no hype here. In my case, I see a marked improvement in how much memory is recovered with Memory Clean when it is used in extreme mode, in contrast to the regular free mode. I now constantly have about 2 GB of free RAM on this 4 GB machine. I imagine that folks with more RAM will regain even more memory.
What I most like is the "Advanced" pane in the preferences. On this pane, you can automate Memory Clean so that it will go into action whenever the free RAM drops below the threshold that you set. It even tells you what is a safe level to set here. Furthermore, you have two options on the "Advanced" pane. One is to enable Auto Clean, and the other is to enable Extreme Mode with Auto Clean. I have both boxes checked.
In short, with the paid version, I don't have to manually clean when the memory drops, as you have to do with the free version of Memory Clean. This "Advanced" pane alone easily makes this app worth the $5.00 that the developer is asking for. For me, it has been a worthy investment. YMMV.
I hope that the developer will continue to maintain and develop this app as new iterations of Mac OS X are released, and that he doesn't let it fall by the wayside. Job well done!