I am thankful that so many people have written reviews of, well, pretty much everything. I always read user reviews, whether I'm buying a bookcase or a book. You can't always believe everything you read, and I know that people have different tastes and what works for one person won't necessarily work for me. But reviews still are useful, especially when you read a lot of them and try to get a consensus. I've written a few reviews myself, but I should probably write more, since I find them so useful myself.
Anyway, I found quite a few reviews about homeschool curriculum. One site which is particularly useful is http://www.homeschoolreviews.com/. This site has reviews of all sorts of curriculum, some dating back years ago, which you have to be aware of since curriculum companies change things over time, sometimes in response to reviews. You can browse by subject category or search for a brand, but the search engine doesn't always work as well as I would like (not finding everything applicable, for instance). Anyway, I've read a lot of their reviews.
Another big site is http://cathyduffyreviews.com/. Cathy Duffy also has a book about her top 100 picks of curriculum. I do find that her website is always rather slow, but maybe it's my connection.
Another site is http://www.successful-homeschooling.com/homeschool-curriculum-reviews.html which I haven't used quite as much. And http://www.homeschoolchristian.com/curricula/reviews/index.php has some reviews of homeschooling methods, such as Charlotte Mason, Classical, etc.
The other main source of reviews for me is retailer websites, such as Amazon and Christian Book (http://www.christianbook.com/). Just search for the curriculum or book you're interested in and usually there are quite a few reviews. I like Amazon in particular since you get reviews from a more diverse group of people usually (not always just Christian homeschoolers - other points of view sometimes give you different insights and more info).
The Christian Book website is really nice, by the way, since they usually have really good prices, plus sample pages of a lot of things. Another homeschool retailer I've ended up buying lots of stuff from is Timberdoodle (http://www.timberdoodle.com/). They have lots of great suggestions for toddlers and preschoolers (things to keep them busy and learning at the same time), and they have great prices too. Almost all the reviews they have are positive ones - maybe those who don't like their stuff don't write reviews? But quite a few of the reviews have good suggestions as to appropriate ages and ways to use the products. The owners of the website have produced quite a few videos they put on the site too, showing how to use a game or toy, for example.
Going directly to the website for a certain curriculum can be helpful too, even if they don't have user reviews, as you can find sample pages or video clips to give you a feel for their material. Many times they will have a table of contents or scope for each course or book too.
The plethora of reviews and samples in the homeschooling world is one reason why I have spent so many hours researching curriculum! There is just so much to review, and so much material to use in reviewing! And you have to sort through conflicting reviews at times and reviews that go against your own beliefs. But it's worth it, in the end, to have a greater certainty that you are picking the right things and not wasting money and time.