I almost agree with Eric ;~). It's a great place to relate your positive experiences, without reservation.
Relating your negative experiences requires much more due diligence, keeping your statements as factual as possible when using the names of product or service providers. This is as much for your protection, as it is for the protection of the supplier. You might later find that your complaint was unwarranted, but the Google archives are forever.
Inquiring minds always want to know, so if it's good, say so, but if it's bad, say so carefully.
For anyone who doesn't know, there are lawsuits in progress against the originators of comments made in a news forum against a supplier. See
http://petsforum.com/psw/