We checked into it with our dog, and unless it is a major medical procedure (ie. Cancer treatment), it really is hard to justify the costs. Our quote was around I think $45.00 a month and it included an annual check-up, but the reimbursement/coverage rates for other procedures was far too low in comparison to actual costs.
As an example, the reimbursement rate for our dog's annual teeth cleaning (we do brush her teeth nightly too) was $200, yet I know our vet charges around $400, so we'd still have to pay $200.00.
Otherwise, it would just be shots/vaccines for the most part. When I ran the numbers, it worked out that we'd be paying $540.00/year in insurance and about $200.00 in other costs. Yet, what we really pay annually is around $600.00 out of pocket for everything.
Also most insurance doesn't cover breed specific traits like hip issues for German Shepards.
All said in done, we just pay out of pocket for everything, in the end, it would take a lot of medicine (even beyond Cancer treatment) to really hurt enough financially that we would need to consider the insurance.