Really disappointed. Reiner is mostly quiet for the duration of the movie, when he speaks, he doesn't say anything that isn't in the "Making of..." featurette. Watch the movie without commentary, see the "Making of" after that, you won't miss anything.

I enjoyed this commentary, especially the bit about him using his mom to play the woman who throws down the punchline immediately after Meg Ryan's fake orgasm. Also the tidbits where Reiner explains how and where the story originated; the people and places who were the inspiration and the people who helped him put it together. Admittedly, this is only for people who truly appreciate Reiner's work. It's not for everybody. There are places where Reiner forgets to keep talking. That's disappointing. Reiner's commentary for Princess Bride is admittedly better. If you have a short attention span, this one's skippable, but if you can stick it out and be patient, there are some precious moments. For example, there's one moment where Reiner talks about the museum scene, and Billy Crystal is improvising, and there's a scant second where Meg looks off camera. This is invisible upon first viewing, but when Rob Reiner points it out to you, Meg is SO breaking character and looking over to him for direction, because Crystal's freaking her out! That discovery alone is worth the price of admission.

I like Rob Reiner as an actor/director, but he gives the WORST commentaries! I can tell from watching him in interviews that he's not a quiet, soft-spoken person. But whenever he watches a film, all he does is sit there and watch. I think he talks for a total of 20 minutes throughout the whole commentary.

This one is not good, but it's not "a complete waste of time", either. Reiner shares some interesting information about the movie, some of it indeed repeated from the "How Harry Met Sally" Making Of, but he speaks in a clear and likable way that scores points for the commentary. He stops frequently to watch the movie, indeed, but to me that wasn't much of a big deal since I, too, often paid more attention to the movie's dialogue than his commentary.
Another certainly better commentary for the movie (on the January 2008 "Collector's Edition" DVD) with Reiner, Nora Ephron and Billy Crystal is available, and probably has already been reviewed by someone on this site, but we we're not very likely to see it because it's probably among the "720 DVDs on the database waiting to be approved".

not informative at all, he talk more about what was going on with his life out of set than about the filming. apparently he fell in love with his wife during the shooting of the movie so he won't shut up about it, it's not bad, I guess it's sort of entertaining but it's the oppositte from informative and I can't beliebe Nora Ephron didn't comment on this.

Look for the When Harry Met Sally DVD / Ws Collector's Edition on dvd.
The commentary with Reiner, Crystal and Ephron is excellent.