I bought this after it was reviewed in a computer magazine. They raved about it, and their step-by-step guide, plus their assurances that there were safety get-outs at several stages for anyone who was nervous about such radical overhauls of applications, reassured me that it was the right thing to do.
Yes, I could probably have saved the $15 by stripping out surplus languages and binaries myself but (a) I'm not savvy or computer-confident enough to do that; (b) I don't have the time or interest, and (c) hey, it's $15. I suspect there are many people like me who just don't need the hassle.
The bottom line? It stripped out 4.72GB of wasted space on a 500GB iMac with 261 applications.
Most impressive were Final Cut Pro 7.0.3 going from 801MB to 183MB; MacFamilyTree dropping from 365MB to 117MB, and Aperture 3.1.3 going from 602MB to 379MB. Also, all the components of the iLife 09 suite slimmed to an average half of their previous size.
I have tried all these applications intensively since the slimming, and I was especially nervous about the hit that Final Cut Pro might have taken having lost 77% of its size. The good news is that everything — even some of the most obscure commands and facilities — seems to be working perfectly.
You could argue that $15 is a lot to pay for 4.72GB of space, but that was only partly why I bought xSlimmer. Subjectively, the heavily slimmed applications are zippier. Much zippier. I also like knowing that there is no padding or dead code on my computer; that it's as lean as it can be.
In short, as a non-geek, all I can tell you is that it has worked beautifully and perfectly for me.

We're getting to the stage where it would take less time just to close the ads than it does to keep installing all these bug-fix updates.