Does anyone have enough trust in Yelp/Trip Adviser et al to use them?

Got no idea. On other review sites, like Amazon, I assume a certain amount of shilling going on. I saw a 5 star software package, and noticed that three of the five reviewers were just overwhelmed by the quality of the packaging. One of the others was favorably impressed by the appearance of the "instructor". I didn't buy it.

Not sure I could spot this stuff on a travel adviser, though.

I love yelp and use the site on a regular basis and for different venues and I
do trust the reviews (at least for my town). So far it has proven to be spot
on - hair dresser, dog groomer, veterinarian, cleaning service, restaurants etc. etc. - I have had nothing but good luck with the site/reviews so far.

I've been using Yelp with great success for about 4 or 5 years now.

I sometimes look at tripadvisor for ideas, then check out the reviews on Yelp. I don't trust the tripadvisor reviews.

perhaps then the problem is that I have been using the wrong site, hopefully this thread will generate enough feedback to tell.

I solve this by taking all reviews with a grain of salt. As I get to know a reviewer in whatever field, I'll give the opinions more weight - or less. I don't know Yelp myself, but I look at not just dozens but hundreds of food blogs, learning what I can, as a kind of hobby. I would trust David Lebovitz, for example, about pastry shops in Paris, should I ever be lucky enough to go there. I'd listen to a2k's Francis about his favorite restaurants there - before I'd listen to a smattering of people I don't know on Yelp or Chowhound or another site I forget the name of, something like "city data".

On the other hand, if I see a lot of consistent complaints about a hotel on one of the travel websites I follow (again, a near hobby), I would take those into account.

I should add, I'd listen to ehBeth on her favorite NYCity places, and several other a2kers on food, since we've all talked together about food for, egad, about a decade now. We might not end up agreeing about the very bestest place, but I'd sure listen if they hated a restaurant.