I actually have used that site before, and I think its pretty good. Its one of the only places I know of that acctually can give you some real world opinions about specific hostels, which can be important since they are all different.

I've stayed at 2 hostels in the US and the reviews of the ones I've been to were fair and accurate.

In terms of staying in hostels, I agree with Nigel, if you are a solo traveler they can be a really good, cheap option, where you can also get to spend some time with other humans who are in a similar situation. However, I also agree that they become less economical with more people. Since they charge per person, the cost for 2 people in a hostel is usually about the same as a cheap motel, and if you've got more than 3 people, a hostel can actually become a more expensive option.