Do a forum search and you'll find lots of threads on this subject. The problem with most of the pet insurance companies is that they don't work like most of our human insurances do. You have to pay the vet first, the file the claim and get reimbursed.
I talked to my vet about Veterinary Pet Insurance (VPI). He says they pay for most things, and that most of their clients who use it like it. However, you'll always hear horror stories about the companies not reimbursing you because of "pre-existing conditions" and what not.
You can check and see if your vet works with CareCredit http://www.carecredit.com/
which is a dedicated credit card for medical expenses, including veterinary costs, that also has a pay back plan on it to make things more affordable. My vet says, however, that they no longer work with them because the people who really need it don't get approved, and those who do get approved can usually find others way to pay.
Having said that, I think pet insurance can be a really great thing if your pet gets into trouble and needs a lot of vet care. I think there are lots of pros and cons with the insurance system the way it is right now, and its just something people have to think about and decide for themselves.