I've heard if applied correctly it does work. Bill Price mentioned it one time. But I recall being at an NWFA show a few years back. It was lunch time with a few hundred sitting down at many large tables. A Murphys rep stopped by each and every one...

You could hear the grumbles at each table she passed trying to promote her stuff...

Here's a You Tube video. Expert Village.

http://www.youtube.com/v/SEtzrq4qU9g&rel=1

As an inspector, I love Murphy's oil soap. Most consumers use it straight out of the bottle without diluting it. Lovely film on the surface that dulls and leaves streaks.
End result: Claims for me to inspect.

I think that is mostly the problem with it. Failure to use is correctly. But consider this also. Think of your floor like a mirror or a piece of glass. If you tried cleaning it with Murphy's, well, you probably will get it clean but you will leave a film of soap, streaks, etc. Most municipal water supplies have salts and minerals that when mixed with a "soap", make that film even worse. So just diluting Murphy's with regular water doesn't help prevent that film on the floors. Now think of wood floor specific cleaners, like BONA Hardwood Floor Cleaner, as more like Windex, only better at cleaning. These wood floor specific cleaners clean as well (or better) than Murphy's and leave no film. And it's the filmy, soapy residue that hinders re-coats and dulls the finish. While it may not "harm" the finish, it just makes it look crappy. Why not just use some generic dish soap instead? Certainly cheaper. Kidding, just kidding. Do NOT use dish soap on your floors. Most, and I mean like 95%, of all worldwide floor finish manufacturers recommend only wood floor specific cleaners like BONA and BASIC. That has got to tell you something.

I get numerous inspections for smudges.

Cleaning lady uses Murphys Oil