I don't have a whole lot to add here, but I'll give you my take. I started taking HMB about 6 years ago when EAS pimped it big time, and the results were decent while cutting, although I paid so much money I dare not think about it again. I've taken it several times in between, but gave up unless it gets dirt cheap sometime soon. But basically as said above, take at least 3g daily on empty stomch while cutting.
I have seen some benefits in muscle sparing while cutting, and it is reported to help increase protein synthesis, although this isn't exactly observeable, so you cn expect to if nothing else retain lean mass while cutting. The absolute best deal I have ever seen on this stuff is from Ultimate Nutrition, around a months supply for 12-15$. There is no reason to pay above this price if one were to actually buy HMB now.
Check out this post at bb.com by Will Brink, very interesting:
Link Removed