Yelp [moved from Boston board]
Yelp is very helpful if you know how to use it (i.e. check the reviewers profile to get a sense of similar tastes to yours) If the user gives McDonalds 5 star reviews and then a 5 star review to Mamma Maria, I tend to disregard their opinion.
Yelp is another tool for me in my CH endeavors. Sometimes a topic will crop up on CH for a reccomendation in a neighborhood and there will be suggestions for specific places but no information regarding why the were reccomended. On yelp, there is sometimes more information as to which dishes to try, best tables to sit at, popular drinks to order etc. I love the photos on Yelp-- especially if someone has taken a picture of the restaurant and it is in an obscure location.
One thing about Yelp is that it tends to be pretty cliquey. I don't mean that in a bad way, but it is what it is. The lively message boards there lend the site to being a dual action review site/social networking site. Sure, CH has message boards, but they're strictly (usually) on focus and not chatting about whatever/whenever.
Also, again not meant in a bad way (I like Yelp), IMO Yelp is oriented towards a younger crowd than CH is. Not that either site is really trying hard to exclude folks, but Yelp seems to have a younger userbase and going for a more "hip" image. The one place where this shows up on Yelp that does kind of bug me (call it more of a love/hate, as I also enjoy it) is their encouragement of off color/funny/etc reviews. Sometimes people go so far out of their way to be witty that you don't get a good sense of what the place is actually like.
In both cases, "it is what it is". They're both useful sites. I tend to use Yelp more for "other stuff" as well as places that aren't solely focused on "the chow". For example, take a place like Charlies Kitchen - it typically gets blasted on this site, but I'm not going there for the most delicious burger of my life. I use CH for a more "food only orientation" when reading reviews.
I definitely agree with the clique-iness of yelp and personally find it pretty off putting. I sill review and read reviews on the site, but I'm not necessarily there to meet people. I find some of the reviews entertaining and some absolutely asinine, but I do appreciate the large mid-20s population. The attitudes and observations of the different spots often coincide with mine, though I similarly use CH as a more authoritative figure on the actual food.
I don't know... that sounds like a lot of work :)
This site rarely (if ever) has led me astray. And from reading many posts by the same person, you get a feeling for their taste and the level of confidence you can have in their reviews. I guess I'll just chalk this one up to different strokes for different folks!